Ten years on, the shadow of the Iraq War looms large over all the party leaders They agree that Syria is different but know that any intervention is doomed to be seen through the prism of Tony Blair's disastrous decision to join the US invasion of Iraq in 2003. They also know that, largely as a result of the Iraq War, voters will be sceptical when politicians promise that any action in Syria will be limited, proportionate and legal and will not suck Britain into another quagmire. Mr Cameron voted for the Iraq War, in his own words, "grudgingly, unhappily, unenthusiastically," but he praised Mr Blair's performance in the crucial Commons debate on the eve of war as "masterful." He even sent constituents who opposed the war copies of the then Prime Minister's speech. Tomorrow afternoon will be Mr Cameron's equivalent of that Blair speech. Although he is not seeking approval for sending in troops, that does not lower the stakes. Many of the bright, independent-minded bunch of 147 Conservative MPs who entered Parliament in 2010 remain to be convinced about the need for any intervention in Syria. As one put it: "We need to see the proof that the Assad regime was responsible. It is not our war. It's a case of "once bitten, twice shy" after Iraq." Some Tories believe the Prime Minister could lose the Commons vote, which would leave him humiliated, weak and unable to join US-led military strikes. Mr Cameron had hoped to win Labour's backing, just as Mr Blair relied on Tory MPs to survive a rebellion by 139 Labour MPs on Iraq. But the Prime Minister's task got much harder tonight when Labour toughened its stance and threatened to vote against the Government. Ed Miliband denied changing his tune but his apparent support for Mr Cameron 24 hours earlier played badly with some Labour MPs. One reason he defeated his brother David for the Labour leadership in 2010 was his revelation during the campaign that he had opposed the Iraq War at the time, when he was not an MP. His retrospective announcement surprised allies of David, who was an MP and voted for it. Mr Clegg voted against the Iraq invasion, which the Liberal Democrats opposed en masse. With hindsight, it looks an easy decision but it was a brave call by Charles Kennedy, the then leader, and some Liberal Democrats had doubts at the time. Mr Cameron has worked hard to ensure a united front with Mr Clegg on Syria. Clegg allies are dismissive of the parallels with Iraq, insisting: "Doing nothing about Assad is still an active choice. It sends a signal to him that using chemical weapons is acceptable. It sets a dangerous precedent. Aides suggest Mr Clegg would not have endorsed any open-ended action designed to topple Assad or put "boots on the ground." But senior Liberal Democrats including the former leader Sir Menzies Campbell have voiced reservations. One party insider said there is "serious concern" about Mr Clegg's stance, claiming he and Mr Cameron have "got carried away" with the success of the Libya operation, just as Mr Blair's success in Kosovo led him down the wrong path in Iraq. More than 10 years on, all roads still lead back to the Iraq War, and for all today's leaders, there is no escaping its shadow.