"All prisoners who participate in purposeful activity must be paid," says Prison Service Order 4460.

That means any inmates employed in work, induction, education, training, or offending behaviour programmes receives a weekly rate.

That rate is not subject to the national minimum wage (£5.52 an hour), so the weekly wage could be as low as £4.

The average is £9.60, usually for a 32-hour week (30p an hour) but their bed and board is paid for.