Tony Blair agreed to commit British troops to battle in Iraq in the full knowledge that Washington had failed to make adequate preparations for the postwar reconstruction of the country.

In a devastating account of the chaotic preparations for the war, which comes as Blair enters his final full week in Downing Street, key No 10 aides and friends of Blair have revealed the Prime Minister repeatedly and unsuccessfully raised his concerns with the White House.

Article continues He also agreed to commit troops to the conflict even though President George Bush had personally said Britain could help 'some other way'.

The disclosures, in a two-part Channel 4 documentary about Blair's decade in Downing Street, will raise questions about Blair's public assurances at the time of the war in 2003 that he was satisfied with the post-war planning. In one of the most significant interviews in the programme, Peter Mandelson says that the Prime Minister knew the preparations were inadequate but said he was powerless to do more.

'Obviously more attention should have been paid to what happened after, to the planning and what we would do once Saddam had been toppled,' Mandelson tells The Observer's chief political commentator, Andrew Rawnsley, who presents the documentary.