The government is to put out to tender all its dedicated juvenile jails that hold children under 18 in a departure in Whitehall's privatisation programme, the Guardian has learned.

The four institutions are to be offered as a job lot to be run by a private prison company in a deal thought to be worth £50m as part of an attempt to boost competition and "choice" in the penal system. It is also thought to be designed to tempt US prison firms into the British market.