How difficult is it to avoid animal products in everyday life?
A vegetarian cafe's decision to refuse the new £5 note sparked a vigorous and sometimes heated debate - and underlined how difficult it is to be a committed vegan in a world awash with animal products.
From going out for a beer to washing your hair or choosing a new car, countless aspects of vegan life involve making a choice about how far principles should trump practicality.
As the row over the new fiver demonstrates - the banknotes had already been in circulation for weeks before it emerged they contained traces of animal fat - living a life entirely free of even the merest animal traces is far from straightforward.
As the Vegan Society states: "To live as a vegan in a non-vegan world takes both courage and curiosity." So just how difficult is it?
Sam East, 44, has been a vegan for 25 years.
She believes people can "only do the best they can" when it comes to avoiding traces of animals in what they eat, or what they use - and she says she will be using the new £5 notes.
"I am not happy about the money but we are foolish as vegans to think this is the only thing that has got past us," she said.
"It's about choice and control - what can I do if it's out of my control?
"Processing film used to use gelatine, so vegans would have unknowingly been doing that for years when they got their photos printed.
"Because we didn't know that, does it make us any less vegan?"
Cambridge cafe controversy
Nestled in an alleyway directly opposite King's College Cambridge, the Rainbow Cafe has long been known as one of the city's veggie and vegan hotspots.
Its owner's choice to stop accepting new £5 note, because the polymer contains a type of animal fat, has catapulted the cafe into the centre of a public debate.
Comments flew back and forth on social media, with one Facebook user posting: "So reject all customers wearing leather shoes, jackets, woolly jumpers & hats etc & go bankrupt!
"Unbelievable that yet again an insane minority is dictating to a sane majority!"
The cafe's owner, Sharon Meijland, said she had simply been making a stand, and had been left "shocked and frightened" at some of the "hatred" she had received online.
Earlier this year, hundreds of thousands of people read a BBC News story about fish swim bladders.
Not a topic regularly on the news agenda, granted - but the story was also about beer, and the gelatine made from fish swim bladders that is widely used to make the drink clear, bright and more attractive.
Certain beers are already approved by the Vegetarian Society, and the Campaign for Real Ale called on other brewers to look for vegetarian and vegan-friendly alternatives.
But brewers are far from the only producers to use animals as part of the manufacturing process.
Winemakers also often use animal products, including gelatine or milk protein, to remove impurities.
Like the new £5 notes, soap, candles, lipstick, crayons and plastic bags can all contain tallow.
Avoiding animal products becomes particularly difficult if you want to buy a car, where they are widely used in all manner of components.
"There's a kind of Bentley that uses 14 individual cow hides," said motoring journalist Ryan McElroy from Car Keys.com.
He wrote an article on which car to buy if you are a vegan after realising there was very little information available.
"Every single vehicle on the road has animal products in - you can't avoid it," he told the BBC.
"Tallow is used to toughen tyres and tubing, steel is coated with lubricants made from animal products, and leather often features heavily in interiors.
"It definitely surprised me, the extent to which things aren't vegan-friendly."
Mr McElroy said Tesla was one company offering an alternative, as it had started manufacturing vegan-friendly models, and an imitation suede product had increased in popularity.
"Paul McCartney got a Lexus kitted out with Alcantara, the faux suede, which is approved by Peta," he said.
"But apparently he was a bit miffed about the carbon footprint when they flew it out to him instead of shipping it."
For many, choosing to avoid animal products is a way of life, and being forced to use a banknote containing tallow is simply unacceptable.
Damian Eade, co-owner of Havant-based ethical vegetarian company Vegeco Ltd, believes the notes contravene the Equalities Act 2010.
"We would never choose to carry products made from animal fat in our pockets. That is being imposed upon us by the Bank of England," he wrote in a letter to the UK's central bank.
He suggests there is a case for indirect discrimination against a religion or belief, saying "a failure to immediately remove the animal fat from new notes and withdraw old ones would be a failure to make 'reasonable adjustment' towards millions of vegetarians, vegans, Hindus, Jains, Buddhists, etc."
Mr Eade said making a legal case would present the hard facts and "take the emotion" out of the argument.
It has been calculated that the total amount of tallow contained in all the new banknotes equates to just over half a cow - but Mr Eade says that to argue there is "just a trace" of animal fat in each plastic fiver "misses the point completely".
"Most people wouldn't feel it appropriate if a restaurant claimed there was only 'trace' of the chef's urine in the soup - or that a trace of child labour in your cheap clothes is not worth worrying about," he said.
But Ms East, who runs a business selling vegan and spiritual jewellery and crafts, said she believed there were more important issues to deal with than the £5 note.
"You can say you're vegan, but if you buy non-organic fruit, it'll be covered in wax sometimes," she said.
"We have to make choices on a daily basis - a holiday cottage I went to this year had a leather sofa in, and I chose to sit on it instead of the floor.
"Nobody can lead this perfect lifestyle. You can only do the best you can, and no-one's going to judge you.
"If you're on a desert island and the only thing you can survive on is meat, what would you do? While I have a choice, I choose the vegan path, but self-preservation always comes through first."