Britain's Home Office is to be split into separate ministries for justice and security.
Home Secretary John Reid is due to answer questions in parliament about the proposals, and the change could happen as soon as May.
Mr Reid - who famously branded the Home Office "not fit for purpose" last year - will be appearing in the Commons after the Conservatives demanded he speak to MPs about the plans.
The division of the sprawling, 225-year-old department would take place after local elections in May, media reports said.
A slimmed-down Home Office would retain control over counter-terrorism, immigration, ID cards, policing and border control.
Prisons and the probation service would join the courts system at the Department of Constitutional Affairs, which would be renamed the Ministry or Department of Justice.
The Home Office employs 77,000 staff, both directly and through agencies including the prison and passport services. Under the plans, Mr Reid would gain day-to-day operational control over Britain's overseas security service, MI6, and its eavesdropping agency, GCHQ, although both would remain under the oversight of Foreign Secretary Margaret Beckett, newspapers reported.
Mr Reid was appointed Home Secretary last year after the mistaken release of more than 1,000 foreign prisoners led to the downfall of his predecessor, Charles Clarke.
But since then the department has continued to be dogged by a series of blunders, including a failure to input details of 27,000 British criminals convicted abroad into the police national computer.