The cross-party consensus over Iraq was broken yesterday when William Hague, the shadow Foreign Secretary, backed Pauline Neville-Jones, the former intelligence chief, in saying the invasion had "failed" to bring about stability after the downfall of Saddam Hussein.
The Tories' shift in stance was provoked by Gordon Brown's visit to Basra during the Blackpool conference and is likely to lead to angry exchanges in the Commons on Monday when the Prime Minister makes his statement to Parliament on troop withdrawals.
Ms Neville-Jones, the former chairman of the Joint Intelligence Committee and now David Cameron's spokesman on intelligence and security, broke the uneasy truce with Labour on Iraq within hours of Mr Brown making his heavily criticised visit to Basra to announce the withdrawal of 1,000 British troops.
She said that the invasion of Iraq had failed and the British-backed coalition had lost the moral high ground. The Tory leadership supported the war on Iraq and has been wary of criticising the Government over the continuing conflict but, after accusing Mr Brown of exploiting his Iraq visit to undermine the Tory conference, the shadow Defence Secretary, Liam Fox, told friends: "The gloves are off."
Mr Hague, who has been more cautious than Dr Fox in attacking the Government, said it was too soon to say Iraq had "failed altogether". But he added: "You can't say it's succeeded. I suppose Pauline Neville-Jones is right in that sense. We have a chaotic situation. In Iraq we still don't have political reconciliation of the political parties in Iraq and there is still a great deal for coalition forces to do there."
He agreed with Ms Neville-Jones that Britain and America had lost the moral high ground. "We backed the invasion but have been very critical of the decisions that have been taken since the invasion.
"We have called over the past year for a major privy council inquiry into the conduct of the Iraq war so that we could learn any lessons for the future."
The decision to go on the attack over Iraq will leave the door open for Mr Cameron to criticise the Government's foreign policy in the region in the run-up to the election.
Mr Cameron said in his keynote speech he would make Afghanistan his priority to stop it becoming a haven again for al-Qa'ida. In a sideswipe at Tony Blair and George Bush, he declared: "We cannot drop fully formed democracy out of a plane at 40,000 feet."
The Liberal Democrat leader, Sir Menzies Campbell, accused the Labour and Conservative parties of "playing cynical political games over Iraq" and said it was time both parties took responsibility for their disastrous military action there.
"It certainly hasn't taken long for a prime minister billed as a statesman to show himself as just another short-term political tactician once a general election is in the offing," Sir Menzies said. "We mustn't allow shallow posturing to obscure the real issue: what possible purpose is served by British troops remaining in Iraq? If their continued presence is merely to provide political cover for the US then the Government must come clean."Reuse content