Beef goulash, Cornish pasties and doner kebabs are all on the menu in British prisons, but if campaigners got their way, inmates would get bean burgers instead of beef burgers.
Its inspiration is "America's toughest sheriff" Maricopa County's Joe Arpaio, who not only makes inmates wear pink underwear and pay for their own food, but has now banned meat in the prisons.
Now Peta has lobbied the chief executive of the UK's National Offender Management Service, telling him follow Arpaio's example - and offered to pay for a vegan chef to prepare a new menu for Her Majesty's Prison Service, an offer roundly rejected by the Ministry of Justice.
Peta Campaign Coordinator Kirsty Henderson said: "Unlike most human prisoners, non-human animals raised for their flesh will never know freedom again.
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"Caged and deprived of all that is natural and important to them, animals incarcerated on today's factory farms rarely – if ever – smell fresh air or feel the sun on their backs until the day they are sent off to slaughter. We hope the Ministry of Justice will seriously consider our offer."
The letter claims a switching to plant-based meals "is a great way to save money and reduce violence" and says it would save money on health care as "vegetarians are less prone to obesity, heart disease, cancer and diabetes than meat-eaters are".
"Earlier this month, we learned that 186 Muslim inmates in UK prisons have launched legal cases in an attempt to win compensation after it emerged that they had been served meals that mistakenly contained pork.
"More than £13 million was paid to inmates last year for mishaps such as these, which could easily be avoided by serving meals free from animal products that people from all faiths can enjoy," the letter added.
A Prison Service spokesperson told HuffPost UK: "In the last two years we have reduced the average cost of prison food by around 11 per cent to £1.96 per prisoner per day.
"Prisoners who want to be vegetarian can be, but we have no intention of enforcing it.”