A van arrives at HMP Edinburgh Prison, Saughton Prison. Picture: Ian Georgeson

The trend, which is costing HMP Edinburgh vast sums of money, is believed to have been sparked by an episode of the popular US prison drama Orange Is The New Black.

Around 13 per cent of the 870-capacity jail’s population is currently on a kosher diet, which is four times more expensive than the regular menu, the report by HM Inspectorate of Prisons for Scotland (HMIPS) says.

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In an episode of Orange Is The New Black which aired in 2015, character Cindy Hayes converts to Judaism as she believes she will get “better quality food” as a result. Kosher food outlaws pork and shellfish and means than meat cannot be prepared next to dairy products.

While regular prison meals cost around £2, the kosher option costs the prison almost £8.

Inspectors said the significant additional cost meant that the trend should be investigated “with some urgency” by the Scottish Prison Service (SPS).

“It was noted that a significant number of prisoners had decided to move onto a kosher diet, which did not appear to be for wholly faith based reasons,” the HMICS report states.

“Given the significant additional expenses of providing this diet, over four times as expensive as the daily food allowance for each prisoner, the SPS should seek to understand the underlying reasons for this development in order to address this situation with some degree of urgency.”