SIR John Chilcot, head of the Iraq inquiry, is expected to get a rough ride from MPs today when he is grilled by the Commons Foreign Affairs Committee over why the investigation has still not reported six years after it began.

Last month, the former Whitehall mandarin, said he could see "no realistic prospect" of publication before the General Election, explaining that it would take further months to complete.

The inquiry has been plagued by delays with lengthy wrangling over what documents could be included in the final report, particularly the correspondence between ex-US President George W Bush and former Prime Minister Tony Blair, as well as the so-called Maxwellisation process of allowing those criticised to respond before publication.

The official probe, into the reasons for the UK's involvement in the 2003 Iraq conflict, began its work in 2009; it held its last public hearing in 2011.