Charities are bidding jointly with the private sector for the construction and running of new prisons in a significant expansion of the voluntary sector's involvement in the criminal justice system, it emerged yesterday.

The penal reform charity Nacro has formed a consortium with the private security company G4S, also known as Group 4 Securicor, in a bid for contracts to be awarded early next year for new 600-bed prisons in Mag-hull, Merseyside, and Belmarsh, south-east London.