A child rapist currently serving 10 years in jail has complained inmates are being "ripped off" for items such as mackerel and olive oil while in prison.
Adam Marchment, who was convicted of raping a 15-year-old girl and sexually assaulting a 14-year-old girl, whined about the prices of food items at HMP Parkhurst on the Isle of Wight after getting a family member to check the costs on comparison websites.
Writing for Inside Times, the weekly magazine for UK prisoners, Marchment said the Prison Service has been "getting away with it" for too long with regards to the costs of food items, which are provided by logistics firm DHL.
He said: "I am really starting to get frustrated by Prison Service responses to the many prisoners complaining about our privatised, over-priced canteen system.
"On Princes.co.uk they state that the RRP for a tin of mackerel fillets in tomato sauce is £1.45, yet DHL sell them to us for £1.75. I also had a comparison website checked and none of the top supermarkets had the same item priced at over £1.40.
"In fact at most supermarkets you can get 4 tins for £5. A bag of Nescafe coffee original 150g, is £2.99, yet DHL sells this item to us for £3.99. Extra virgin olive oil is £1.99 for 500ml, but DHL sell us 250ml for the same price. Are you seeing the recurring pattern?
"DHL continue to rip us off and are getting away with it. It is about time HM Prison and Probation Service [HMPPS] stopped ignoring this situation and realise that prisoners have access to the outside world and will question the utter rubbish they try to feed us."
An HMPPS spokesperson said they were "mindful of the need to provide value for money to the taxpayer in all our contracted services" adding that "all public sector prisons must operate a cost-neutral contract, at no cost to the public".
A Prison Service spokesperson said: "Products sold through the prison canteen service are never higher than the manufacturer's recommended retail price."
Marchment was jailed in April 2016 following the attacks in September 2015 and July 2014. While on the run from police, he mocked police by posting Facebook updates detailing how long he has evaded capture.
In one post, Marchment said: "Hello everyone, I'm Adam Marchment and as you all know I am a wanted man. I have now been on the run for 37 days.
"I've got a little message for Surrey, Sussex and Hampshire Police - 'run run as fast as you can, you can't catch me I'm the Marchment man'."
Marchment even sent a photograph of himself stood outside a police station to local press before he was eventually arrested on 14 October 2014.