A central plank of Tony Blair's plans to overhaul Britain's creaking criminal justice system was thrown into disarray last night when leaked Home Office documents passed to The Observer revealed that the moves could lead to the release of dangerous criminals with inadequate supervision.

A series of assessments prepared by the Government's own civil servants show they believe there is a 'very high' likelihood that flagship plans to merge the prison and probation service will put the public at risk from violent criminals.