In November 2016 the new fiver, which entered circulation in September, was found to contain minute amounts of animal by-product, tallow. The fatty substance is used in the production of polymer pellets used by Innovia Films in Wigton, Cumbria, to create the banknote substrate. The notes are printed by De La Rue.

The public backlash from vegans, vegetarians and religious groups, that followed its discovery forced the Bank of England (BoE) to consider alternative options.

The BoE stated at the time that it had not been aware of the inclusion of animal derivatives in the new notes. As a result of the polymer outcry, the bank also investigated its paper stock and discovered that although no animal derivatives could be traced on finished paper notes, one animal-derived ingredient is in fact used in the recycling of off-cut materials.

In a statement issued this morning the BoE said it had now concluded the it would be “appropriate” to keep the existing £5 polymer notes in circulation and push ahead with the new £10 note roll-out planned for September this year.

It said further opinions would be sought on the use of animal derivatives and plant-based alternatives before further production runs of the £5 and £10 notes and before production begins on the new £20 note, which is slated to enter circulation by 2020.

The Bank also said it had delayed the signing of contracts with its supplier for materials to be used in the production of the polymer £20 note. Stocks for further print runs of the current paper £20 and £50 notes are due to run out in July this year, however the bank has confirmed that if and when it does re-order "materials containing animal-derived residues will not be included in any recycling processes". 

The statement said: “In reaching its decision, the Bank has given careful consideration to the possible alternative options for the current £5 note and the Jane Austen £10 polymer note.”

Considerations included in its assessment were: the complexity of production; ensuring enough stock is kept in circulation; and the effects of delaying production of new denominations.

The statement said: “Producing banknotes is complicated. A variety of processes are required to manufacture a secure note of the highest quality, and the lead times involved are therefore significant.

“Production of the new £10 polymer note began last August and the Bank has already printed 275 million notes, at a cost of £24 million, ahead of planned issuance later this year.

“The Bank has also spent £46 million on printing the £5 polymer note. Reprinting these notes on a new substrate would mean incurring these costs again. It would also require a further £50,000 for the secure destruction of the existing stock.

“The Bank works hard to ensure that the public has enough secure notes to use in daily life and destroying the hundreds of millions of notes already printed would put this at risk. The Bank cannot guarantee sufficient stocks of paper notes to replace the destroyed polymer notes.

“Delaying the issuance of the polymer £10 would also delay the benefits of the increased counterfeit resilience of polymer being achieved for the Bank and the public.

A spokesman for Innovia Films said that its investigations were ongoing.

He said: “Innovia Security has been in discussions with its suppliers who are working across the supply chain to investigate any non-animal based alternatives that could be used in the manufacture of the resin used to make polymer banknotes.”

On 30 March the BoE will launch a consultation into the content of its future banknotes, the results of which will be published in the summer along with its proposals for future production.