By Raakhi Odedra and Stuart Cooper (Notes Directorate).footnote 
- Our first polymer banknote series is now complete.
- We moved to polymer to make banknotes cleaner, safer and stronger. Early indications are that these objectives are being met already. In particular, because the new banknotes are much more difficult to copy, counterfeiting levels have already fallen significantly.
- Innovations in the manufacturing process have also helped to improve efficiency, reduce waste and reduce our carbon footprint.
- Despite changes in the way people shop, and the increased use of digital payments, cash remains an important payment option for many people. The Bank of England will continue to produce banknotes to meet demand from the public and has an ongoing research programme to support this.
The Bank of England is responsible for producing and issuing banknotes in England and Wales.footnote  Our most recent series of Bank of England banknotes, technically known as Series G, was launched over a five-year period between 2016 and 2021.footnote  This series is the first that we have printed on polymer.
This article provides historical background on the evolution of banknote design and security features and explains how our new banknotes are cleaner, safer and stronger. It also outlines the key stages of issuing the latest series, from design to launch, which is followed by the withdrawal of legal tender status of the old paper series banknotes.
Figure 1: Banknote launch timeline
Introduction: the rationale for a new banknote series
Banknote design through the ages
Money has a long and fascinating history. Early units of exchange included seashells, livestock, precious metals and commodities. Paper money was first introduced in China in the 7th century. In Europe, Sweden was the first country to issue banknotes in 1661 and the Bank of England started issuing banknotes that were ‘payable to bearer’ soon after it was established in 1694.
It was – and remains – our job to ensure banknotes are secure and that people can trust them as a means of payment. Since their initial introduction, our banknotes have changed significantly in terms of size, design and security features.footnote 
You can see how the overall appearance of banknotes has evolved in Figure 2. Early banknotes were monochrome…they were also very large! For, example, the £50 issued in 1943 was more than twice the size of our latest £50 issued in 2021.footnote 
Gradually banknotes have become more sophisticated, incorporating more colour, more complex designs and security technology. They also became smaller, to make them more convenient to use.
Figure 2: The design of Bank of England banknotes has become more sophisticated
- Source: Bank of England.
As you can see in Figure 2, early banknotes in the 18th century appear simple by today’s standards, although they did incorporate the best security features available at that time.
Some of the early security features are quite intriguing. The Britannia designs used on notes from 1761 were very slightly different on each denomination, the idea being that these tiny variations in design would not be noticed by counterfeiters. They were of course known to Bank of England clerks who could use them to verify and accept the notes.
As printing techniques improved over time, the designs became more complex and harder to copy. This included the introduction of machine tools, known as lathes, to produce ‘guilloche’ patterns. An example of these patterns, from a development trial of the Series B banknotes in the 1950s, is shown in Figure 3. For a time, we employed skilled workers who operated the lathes to produce these complex images. With the advent of modern printing techniques, their value as a security feature has reduced, but they are still a feature of banknote design, being a part of the design aesthetic that the public easily recognise and trust.
Figure 3: ‘Guilloche’ patterns were first used as a security feature, but have remained a part of banknote design
- Source: Trial design by Stephen Gooden, 1954–55. Bank of England Museum accession 1979/035/055. © Bank of England.
One of the key security features recognisable to the public, rather than just bank clerks – and used right up until the last paper banknote series – was the watermark. Originally made by pouring cotton mulch over a copper mesh to make paper dry in alternating thicknesses, the technique has developed since, but the essence remains the same. Patterns show up through the paper when held to light, making it difficult for a counterfeiter to replicate.
Evolution of more sophisticated security features
Banknotes have always run the risk of being copied, but technological advancements in the latter half of the 20th century, which enabled the widespread introduction of colour photocopiers and desktop printers, meant that complex designs and watermarks were no longer enough to protect the currency against counterfeiting.
This spurred further waves of innovation and more sophisticated security features have been developed to stay ahead of new counterfeiting threats.
An example of this came in 1984 when new types of ‘windowed’ metallic thread were introduced as part of the design of Series D. While solid metallic threads had been used on our notes since 1940, this new design of thread appeared dashed until it was held up to the light. Importantly, if the note was photocopied, the thread would show as a solid line, which would clearly identify a copy. Further advances were made in Series E, when the foil patch, ultra-violet feature and micro-lettering were used for the first time on Bank of England banknotes.
Series G design and security features
In 2011, our banknote designers and scientists began work that, in collaboration with the manufacturers and relevant suppliers, would shape the design and features of the new banknote series.
The main aims for the new series were to make banknotes stronger and more secure, and for notes to also stay cleaner in circulation. The process of designing and trialling the first banknote in a new series – especially where substantial changes in the design or technology are involved – can take several years. The process involves scientific research on new materials and security features, incorporation of accessibility features, producing an overall design concept, and detailed engraving work. Only after this phase is completed does manufacturing trialling and full production begin.
The decision to switch to polymer
The decision to switch to polymer banknotes was the result of a comprehensive assessment of the durability and security of different materials by our scientific experts, as well as outreach with the banknote industry and the general public.
As part of our own assessments, new banknote materials were subjected to a range of chemical and physical tests to assess their durability; including being put through the Bank of England washing machine (they survived!). This demonstrated that the new polymer banknotes would be much stronger and more durable than the previous series. The polymer material itself is also inherently more secure, both in terms of the difficulty of printing on it in large volumes and the ability to incorporate large intricate windows that are more resilient to counterfeiting.
The inherent security of polymer has been evidenced by the international experience of the introduction of polymer in other countries. Chart 1 shows how counterfeiting levels in Canada fell significantly when it introduced polymer notes in the early 2010s and those levels have remained consistently low since. The additional durability of polymer banknotes was also apparent from other countries’ experience.
Chart 1: The impact of introducing polymer banknotes in Canada
- Source: Bank of Canada.
As part of the early engagement on the design of the new series, we held focus groups with members of the public to help us test the handling and practical use of the new banknotes. We also held regional roadshows in shopping centres across the country to engage the public, and our polling showed that 87% were in favour of a switch to polymer banknotes. Overall, the switch to the use of polymer material was judged to support improvements in banknotes, including their durability, which would strengthen the public’s confidence in the currency.
Selection and design of security features
The new series incorporates our most advanced security features, developed with our suppliers as part of our long-term banknote research programme.
Our scientists first assess how resilient different security features are to counterfeiting techniques. As well as being difficult to replicate, security features must also be easy to use and intuitive. As part of the research for the new banknote series, we ran psychological perception studies to ensure that the new security features being considered were easy to recognise and check .
Based on this research and development, we have incorporated a number of security features that are common across all the denominations in our new polymer series to make checking easier. In addition to the inherent security of polymer material (as described above) and the use of an ultraviolet (UV) feature and micro-lettering as used on our paper notes, the notes have a foil applied that contains a number of different security features. These include a hologram that changes from one image to another when tilted from side to side and a silver foil patch that contains a 3D image of the coronation crown. It also includes highly detailed metallic images over the see-through window, which are different in colour when seen from the front and back of the note. In addition – taking advantage of the see-through windows which are possible to incorporate in polymer notes – there is a finely detailed image of Her Majesty Queen Elizabeth II in the window; analogous to the watermark image on paper notes.
You can take a closer look at a number of the key security and design features used in our new £50 in Figure 4.
Figure 4: Explore our polymer £50 note
Key security features
Focus on these two key security features to help confirm that your notes are genuine:
Tilt the note from side to side. Check the words change between 'Fifty' and 'Pounds'.
See through windows
Look at the metallic image over the main window. Check the foil is gold and green on the front of the note and silver on the back. Within the two gold foil squares on the front of the note, the image changes between '50' and a '£' symbol when the note is tilted.
Look for a second, smaller window in the bottom corner of the note.
Other security features
The Queen's portrait in the see-through window
A portrait of the Queen is printed on the window with '£50 Bank of England’ printed twice around the edge.
Silver foil patch
A silver foil patch contains a 3D image of the coronation crown. You will find this above the main see-through window on the front of the note.
Red foil patch
A metallic, red foil patch contains the letters 'AT'. You will find this on the back of the note, directly behind the silver crown on the front of the note.
Feel of polymer and raised print
The note is printed on polymer, which is a thin and flexible plastic material. On the front of the note, you can feel raised print. For example, on the words ‘Bank of England’ and in the bottom right corner, over the smaller window.
The printed lines and colours on the note are sharp, clear and free from smudges or blurred edges. If you use a magnifying glass, you will see the value of the note written in small letters and numbers below the Queen's portrait.
Under a good quality ultraviolet light, the number '50' appears in bright red and green on the front of the note, against a duller background.
Banknotes must be practical for everyone to use. So our banknotes are designed to include features to help visually impaired people identify and use the notes. Printed features, such as large numerals, high contrast and strong colours are important for partially sighted people. Differential note sizes are also a helpful design feature for people with no vision. As part of the research for the polymer series, we worked with the Royal National Institute of Blind People (RNIB) to consider the development of additional features to aid accessibility. Based on this collaboration, this is our first series to include an embossed tactile feature, which is made from a series of clusters of four raised dots positioned on the left-side edge of the banknote. The number of clusters varies on each denomination to enable blind and partially sighted users to differentiate each denomination value.footnote  The incorporation of this tactile feature was only made possible due to the use of the new polymer material. Due to its plasticity, polymer is much more able than paper to keep the shape of this feature.
The introduction of each new banknote series brings an opportunity to develop new exciting designs that will appeal to the public. However, for ease of making payments, people also need to be able to easily recognise and check their banknotes.
So it can be helpful to keep some elements of continuity in design to keep the currency recognisable, and to support public acceptance. Keeping some familiarity in design has been particularly important when making the transition from paper to polymer banknotes. Key design features that have been carried over from previous banknote designs into the polymer series include the Bank of England font and an unchanged portrait of Her Majesty Queen Elizabeth II on the front of the banknotes. The front of the banknotes are very similar across all denominations. This is also important because it makes the series recognisable as a set.
As part of the Bank of England banknote design, the character that appears on the back of the banknote is the main way that each individual denomination is differentiated. We provide background on the character selection process in Box A.
In addition to being easy to recognise, and easy to use, the finished design must also be possible to produce in large volumes of banknotes to a high-quality standard.
Working to these principles, our banknote designers were responsible for creating a design concept for each banknote in the new series. Concept designs provide an early sketch of how the character and design elements would be set on the finished banknote. When creating this design concept, our designers consider images, style, text, size and colour.
Once the concept is agreed, the next stage of the design process is to integrate the security features within the design. These need to be brought together in a way that is both aesthetically pleasing and practical. The concept image is then translated into a detailed design, using fine lines, dashes and patterns to depict the portrait and supporting images, all portrayed in the main denomination colour for each banknote. When you look closely at our latest banknote series, you will see much more than the character and security features. The visual design incorporates many images inspired by the character’s achievements and work. For example, the design of the new £50 featuring the scientist and mathematician Alan Turing, incorporates the Automatic Computing Engine Pilot machine, mathematical formulae, and binary code, as well as his portrait.
Engraving for printing plates
The more detailed design process for a banknote needs the expertise of specialist graphics technicians, using various printing techniques. Traditionally, engravers would create portraits and other elements of the banknote design by hand. They engraved the images onto metal plates which would then be reproduced as printing plates for the intaglio process (Figure 6). Today, much of the design work is done using specialist computer-aided design and this software also helps to make the industrial production tools, including printing plates. However, despite all the advances in technology, the engraved images needed for part of the printing process have to be produced first by hand at a scale five times larger than the finished note size in order to incorporate the fine detail required for mass production.
Box A: Banknote character selection
Banknotes are money, but they are also little artworks in our pockets. They can be a symbol of identity and nationhood and, as such, designs are constantly evolving over time. Across the world, banknote designs commonly incorporate people, iconic landscapes, buildings and nature.
Images of monarchs have been used on UK coinage for hundreds of years but have only been a key part of the design of Bank of England banknotes over the past 60 years. Her Majesty Queen Elizabeth II became the first monarch to appear on a banknote in 1960. And since 1970, Bank of England banknotes have also featured important historical characters on the reverse side.
Traditionally, the Governor of the Bank of England has decided which characters appear on new banknotes. In 2015, we used a new character selection process for the first time for our latest £20 banknote, asking the public to nominate the visual artist they wanted to see on the design. The Banknote Character Advisory Committee, which includes both external members and Bank of England staff, shortlisted a number of characters. Based on this shortlist, the Governor of the Bank of England at the time, Mark Carney, chose the painter J M W Turner to appear on the £20.
We invited the public to participate again in 2018 for the new £50, based on the theme of science. There was an unprecedented response. This time, the call for public input attracted over 225,000 nominations for 989 characters which spanned the full breadth of scientific endeavours, from astronomy to physics, chemistry to palaeontology and mathematics to biochemistry. From these nominations, the scientist Alan Turing was chosen as the character on the £50 banknote.footnote 
The recent launch of the £50 banknote was an important landmark. Alan Turing is the first known LGBTQ+ figure on a Bank of England banknote. He made a huge contribution to the fields of maths, computing and science more broadly. He also suffered great injustices as a gay man.
The mission of the Bank of England is underpinned by a responsibility to promote the good of the people of the United Kingdom. As we look to the future, the design of banknotes will continue to evolve, both in terms of security features and design. Given the importance of banknotes as symbols of the UK’s values and achievements, it is important that this is properly considered, that the public are involved in making these decisions, and that we continue with our efforts to ensure a balance of diversity and representation. The Bank of England will continue to comply with its obligations under the Equality Act 2010 and consider all protected characteristics and diversity more generally during any future banknote design process.
As well as needing to withstand day-to-day use by the public, retailers and processing at cash centres, we also need to be sure that a banknote’s design and security features can be mass-produced.
For the polymer series as a whole, at the time of writing we had printed almost six billion banknotes, all produced to exacting standards, including specifications on size and quality of each key component. The move to polymer and addition of more sophisticated security features meant that the production process was also more complex. Up to one and a half years of pre-production trials were required for each new banknote to optimise the previously agreed design for the manufacturing equipment and industrial scale production. Throughout this stage, our technical experts, the printer, and the suppliers of polymer and security features had to work together closely.
Another innovation for the polymer series was the procurement and supply-chain strategy for the polymer substrate itself. When we started production work on our new series in 2014, we used a single supplier of polymer material for banknotes, CCL Secure,footnote  which provided the material for the £5 and £10 banknotes. However, from the introduction of the new £20 and £50 banknotes, the material for all banknotes has been sourced from two suppliers, CCL Secure and De La Rue. This dual supply strategy supports ongoing price competition, removes the risk that the supply of polymer material is dependent on a single source, and has also allowed us to work with both suppliers to deliver other efficiency and environmental benefits, such as a reduction in the carbon footprint of the polymer material. Initially, CCL Secure produced the polymer in Australia but committed to build a new UK manufacturing plant in Wigton, Cumbria. The way the polymer film is made at this new site is remarkable to see, as it is formed by creating an enormous bubble (Figure 5). De La Rue uses a different production method to manufacture polymer film to our specifications.