The government has announced that Britain's intelligence machinery is being overhauled after the mistakes it made about Iraq's weapons of mass destruction.

MI6 will ensure that information from foreign spies is checked more thoroughly, while the Cabinet Office department dealing with intelligence is to be substantially expanded.

Ministers and officials will also be issued with new guidelines warning them about the "limitations of intelligence".

Jack Straw, the foreign secretary, unveiled the reforms in a statement setting out the government's response to last year's Butler report on the Iraq intelligence failings.

Straw said that MI6 had appointed a senior officer "to oversee the quality of reporting, the underlying intelligence processes and the effective evaluation of sources".

Tony Blair has also pledged that small groups brought together to work on military planning will operate formally in future as ad hoc Cabinet committees.