When the Bank of England launched its new polymer five pound banknote a few months back, it was highlighted as being strong, resistant to moisture and dirt, and better for the environment. But no mention was made of it containing fat… animal fat that is.
This week, the BoE confirmed on Twitter that its new £5 banknote contained a "trace of tallow", a substance which comes from animal fats, including rendered forms of beef or mutton.
"We can confirm that the polymer pellet from which the base substrate is made contains a trace of a substance known as tallow," the Bank of England, said in a statement emailed to CNBC.
"Tallow is derived from animal fats (suet) and is a substance that is also widely used in the manufacture of candles and soap."
The news caused upset amongst British vegans, vegetarians and religious groups, and even triggered an online petition asking the central bank to remove the tallow. The Change.org petition has received more 97,500 signatures.
"The new £5 notes contain animal fat in the form of tallow. This is unacceptable to millions of vegans, vegetarians, Hindus, Sikhs, Jains and others in the U.K.," the petition reads, asking the institution to cease the use of "animal products in the production of currency that we have to use."
The new five pound note — which features Sir Winston Churchill — marked a new stage for the U.K. currency, due to its polymer material. Prior to the introduction of the £5 note in September, all other notes in current circulation have been made out of paper.
Bank of England is taking this issue 'really seriously'
Following the tallow update, several individuals took to Twitter to express their fury, while leading organizations and religious groups also weighed in on the debate.
"(Tallow) doesn't need be used in the notes at all as there are many plant-based alternatives," Ali Ryland, a spokesperson from The Vegan Society, said in a statement emailed to CNBC.
"Using animals in this way is outdated and unnecessary, not to mention the fact that it is obviously cruel. While vegans will be unable to opt out of using these notes, we hope that the Bank of England and their supplier take this seriously and use alternative, vegan-friendly sources for all future notes," Ryland added.
Meanwhile, a spokesperson from the Board of Deputies of British Jews said that while Jews are not allowed to consume tallow, they are allowed to handle it, adding in a statement emailed to CNBC that "the new £5 note won't be problem for Jews unless they attempt to eat them."
When it comes to the issue of using tallow, Lynne Elliot, the CEO of The Vegetarian Society, said it wasn't necessarily an issue for those who follow a vegan/vegetarian diet for their own personal health; however it may be "a massive issue" for those who choose this diet because they are concerned about animal welfare.
"I think that's really just because people take a lot of care and effort to try and avoid using products that are from animal slaughter, in their life," Lynne Elliot, The Vegetarian Society's CEO, told CNBC over the phone.
"So they're very careful about what cosmetics, cleanings products, clothing they use and they've got choices about all those things."
"But this is going to be very difficult for people to avoid using the currency of the land."
Elliot added that the Bank of England had been very supportive of the situation, after the society spoke with the central bank on Tuesday night.
"(The Bank of England) are taking this issue really seriously. They are listening. They are understanding that it's really concerning some people. They've set off to do a full investigation now," Elliot said.
The next two banknotes set to enter circulation soon are both—at present—expected to be made out of polymer: the polymer Jane Austen £10 banknote due in 2017, and the J.M.W. Turner £20 banknote, due out by 2020.
"I'm really, really hoping we might be able to find an alternative going forward," Elliot added.
Follow CNBC International on Twitter and Facebook.