A cross-party alliance of MPs is pushing for Tony Blair to be declared guilty of “contempt” towards Parliament over the Iraq War – as calls for legal action against the former Prime Minister grow. A parliamentary motion, being tabled this week subject to approval by the Speaker, will declare that Mr Blair used “deceit” in the run-up to the invasion. Its proponents say it could see him barred from public office and stripped of his privy council position.

Labour leader Jeremy Corbyn today signalled his backing for the motion, urging MPs to examine evidence suggesting that Mr Blair had misled Parliament over the invasion. The parliamentary device, to be formally proposed by outspoken Conservative MP David Davis, has attracted the backing of MPs from Labour, the Tories, Scottish National Party, Green Party and Plaid Cymru.

The landmark Chilcot inquiry, which, since 2009 had been investigating the circumstances of the invasion, said last week that Mr Blair’s intelligence case for the attack on Iraq was “not justified” by the facts. Mr Corbyn’s backing for the motion comes after John Prescott, the Deputy Prime Minister at the time of the invasion, said Mr Blair had led Parliament into backing an illegal war.

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“I urge colleagues to read the Butler report and the Chilcot report about the way Parliament was denied the information it should have had, the way there was lack of preparations for the conflict’s aftermath, and the way in which assertions of weapons of mass destruction [were made],” Mr Corbyn told BBC One’s Andrew Marr Show. “Parliament must hold to account, including Tony Blair, those who took us into this particular war. That is surely how a parliamentary democracy works. I haven’t seen [the motion] yet, but I think I probably would [back it].”

The Liberal Democrats, who opposed the war on the basis it did not have United Nations support, have also not ruled out backing the motion. The Independent understands that the party’s MPs will be meeting on Monday to discuss their position. Other supporters include former Scottish first minister Alex Salmond, who has long opposed the war, and Plaid Cymru MP Hywel Williams. Green MP Caroline Lucas, who is supporting the contempt declaration, said the Chilcot report was “a damning indictment of Blair’s record”.

“It showed that the former Prime Minster actively deceived Parliament and led this country into a disastrous and bloody war under false pretences,” she said. “I’m joining with fellow MPs to hold Blair to account by tabling a contempt motion which could see him barred from public office and have his privy counsellorship stripped from him.” Mr Blair’s office declined to comment on the motion when approached by The Independent. However, Dame Margaret Beckett, a close supporter of Mr Blair, said: “The Chilcot report was never going to settle the arguments about the war.

“The people behind this contempt motion were always going to use the Chilcot report for their own ends. It is, however, very clear from the Chilcot report that Tony Blair did not lie, did not falsify intelligence and that the Cabinet was not misled on the presentation of the legal advice. As a member of the Cabinet at the time, I am clear that the Attorney General provided a clear legal basis for military action which was consistent with all the information with which Cabinet had been presented on a regular basis over the previous weeks.”

Shape Created with Sketch. In pictures: Families of Iraq War victims react to Chilcot report Show all 10 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. In pictures: Families of Iraq War victims react to Chilcot report 1/10 Relatives and friends of the military personnel who died in Iraq, leave the Queen Elizabeth II Conference Centre PA 2/10 Dawn Holmes, the mother of L Cpl Sarah Holmes who died in Iraq, is consoled by solicitor Matthew Jury as she leaves the Queen Elizabeth II Conference Centre PA 3/10 A family member holding a photograph of Stephen Robert Wright (R), outside the Queen Elizabeth II Conference Centre, after the publication of the Chilcot inquiry into the Iraq War PA 4/10 Families of soldiers killed in the Iraq conflict stand together outside the Queen Elizabeth II conference centre after the outcome of the Chilcot report Getty Images 5/10 Relatives of military personnel killed during the Iraq War talk at a news conference after listening to Sir John Chilcot present The Iraq Inquiry Report at the Queen Elizabeth II Centre in Westminster Getty 6/10 Relatives of military personnel killed during the Iraq War react after listening to Sir John Chilcot presenting The Iraq Inquiry Report at the Queen Elizabeth II Centre in London AP 7/10 Relatives and friends of military personnel killed during the Iraq War attend a news conference after listening to Sir John Chilcot present The Iraq Inquiry Report at the Queen Elizabeth II Centre in Westminster Getty Images 8/10 Family of those who died in Iraq speak to the media as they leave the Queen Elizabeth II Conference Centre in London PA 9/10 Relatives and friends of military personnel killed during the Iraq War attend a news conference after Sir John Chilcot presented The Iraq Inquiry Report at the Queen Elizabeth II Centre in Westminster Getty Images 10/10 Victoria Jones (L), a relative of a British soldier killed in Iraq, holds a copy of The Report of the Iraq Inquiry, by John Chilcot, at the Queen Elizabeth II centre in London Reuters 1/10 Relatives and friends of the military personnel who died in Iraq, leave the Queen Elizabeth II Conference Centre PA 2/10 Dawn Holmes, the mother of L Cpl Sarah Holmes who died in Iraq, is consoled by solicitor Matthew Jury as she leaves the Queen Elizabeth II Conference Centre PA 3/10 A family member holding a photograph of Stephen Robert Wright (R), outside the Queen Elizabeth II Conference Centre, after the publication of the Chilcot inquiry into the Iraq War PA 4/10 Families of soldiers killed in the Iraq conflict stand together outside the Queen Elizabeth II conference centre after the outcome of the Chilcot report Getty Images 5/10 Relatives of military personnel killed during the Iraq War talk at a news conference after listening to Sir John Chilcot present The Iraq Inquiry Report at the Queen Elizabeth II Centre in Westminster Getty 6/10 Relatives of military personnel killed during the Iraq War react after listening to Sir John Chilcot presenting The Iraq Inquiry Report at the Queen Elizabeth II Centre in London AP 7/10 Relatives and friends of military personnel killed during the Iraq War attend a news conference after listening to Sir John Chilcot present The Iraq Inquiry Report at the Queen Elizabeth II Centre in Westminster Getty Images 8/10 Family of those who died in Iraq speak to the media as they leave the Queen Elizabeth II Conference Centre in London PA 9/10 Relatives and friends of military personnel killed during the Iraq War attend a news conference after Sir John Chilcot presented The Iraq Inquiry Report at the Queen Elizabeth II Centre in Westminster Getty Images 10/10 Victoria Jones (L), a relative of a British soldier killed in Iraq, holds a copy of The Report of the Iraq Inquiry, by John Chilcot, at the Queen Elizabeth II centre in London Reuters

A spokesperson for the group of MPs organising the censure motion said parallel legal action threatened by families of soldiers who served in the Iraq War could proceed separately to their efforts. “This initiative does not interfere in any way with legal action either by the authorities in terms of criminal law or by the service families in the civil courts. However, there is a specific parliamentary matter of holding the former prime minister to account given the revelations in Chilcot,” the spokesperson said.

“Most damning of all is the detailing of what Blair was promising US President George W Bush in private memos while he was telling Parliament and people something entirely different in public statements.

“If we are to prevent such a catastrophe happening again it is essential that parliamentarians learn to hold the executive to critical examination in a way that Parliament failed to do in 2003. Holding Blair to account will be an essential part of that process of parliamentary accountability. The case has been made by Chilcot and any Parliament worth its salt is duty bound to take action.”

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At a press conference last Wednesday, families of some of the British soldiers killed in Iraq said they “reserve the right to call specific parties to answer for their actions in the courts”. Roger Bacon, whose son Matthew died when his Snatch Land Rover was hit by an improvised explosive device in Basra in September 2005, named Mr Blair as someone who might face legal action.

The 2.6 million-word Iraq Inquiry report was finally released last Wednesday around seven years after its launch was announced by Gordon Brown. Overall, Sir John Chilcot, the investigation’s chair, was damning in his verdict on the invasion. “We have concluded that the UK chose to join the invasion of Iraq before the peaceful options of disarmament had been exhausted. Military action at that time was not a last resort,” he said.

“We have also concluded that the judgements about the severity of the threat posed by Iraq’s weapons of mass destruction were presented with a certainty that was not justified. Despite explicit warnings, the consequences of the invasion were underestimated and the planning for Iraq after Saddam Hussein were wholly inadequate.”