Last month, Channing Wood prison in Devon won the grounds maintenance contract from Denbury primary school with a tender bid of £800. Union officials believe the prison submitted its bid partly because of pressure from the Home Office to find additional work for its inmates.
'The idea that the Home Office is sending out letters to its prisons telling them to get involved in CCT is very worrying,' said Richard Jewison, Unison's regional head of local government for the south-west.
'There are serious jobs issues, safety issues and civil rights issues at stake. When they did that sort of thing in China, there was outrage on a grand scale.'
Until the end of last year, private contractor Brophy held the contract for the school along with the county's other schools. But when it came up for renewal, the school decided to seek a contractor independently.
According to head teacher Len Peach, the governors decided to award the contract to the prison because of the quality of work, even though its bid worked out as £50 more expensive than the bid from the county council's DLO.
John Roberts, director of the Association of Direct Labour Organisations, also expressed concern about the developments. 'If they let Strangeways prisoners out into the schools in Salford, they are likely to get beaten up,' he said.