Tony Blair has backed David Cameron’s call for Britain to take military action in Syria, declaring that “many Labour MPs” agree with him.
The former Prime Minister told an event hosted by comedian Matt Forde - and to be broadcast on Friday - that it was “it was important we take strong action against ISIS” in their main base.
Speaking at 'The Poltical Party' event at St James' Theatre, London, Mr Blair also hinted that while there had to be a ‘transitional’ period to keep Assad in power while the Islamist terrorist were tackled, the West should be prepared to commit to anti-Assad forces over the longer term.
His comments came as Shadow Foreign Secretary Hilary Benn told the BBC that there was now a 'compelling case' for Syria action.
Earlier, Mr Cameron sought to persuade Labour and Tory MPs to back RAF airstrikes in Syria, with his seven point plan in the Commons.
But Jeremy Corbyn struck a markedly sceptical tone, raising key questions over the legality of any new action and the military and diplomatic hurdles yet to be overcome.
The intervention from Mr Blair - who famously claimed that Corbyn supporters need a 'heart transplant' during the Labour leadership campaign - may bolster some Labour Shadow ministers, but it could also backfire given his reputation in the new party membership.
In his interview, Mr Blair said: “I would support the position that has been set out, not just by David Cameron, but by many Labour MPs.
“I think it’s important that we take strong action against ISIS and take that action against them where they are headquartered, which is in Syria, so obviously I would support that.
“But this is going to be a long hard struggle, not just against ISIS in Syria, but you have got ISIS, you have got Jabhat al-Nusra, you’ve got Al Qaeda, you’ve got al-Shbaab, you’ve got Boko Haram, you’ve got these groups that have proliferated all over the world.
“Tthis is the biggest security challenge of the 21st century and it’s going to take a long time to defeat it and you have to defeat a number of different levels. “
Asked if there should be military intervention against Assad too, Mr Blair said that the country would need a new constitution but hinted the West should support those who wanted rid of the Syrian leader.
“The issue in respect of Assad is whether he is going to be forced out over a period of time, because the majority of people in the country who have been excluded from government and who have now been subject to this absolutely brutal campaign where over 300,000 people have lost their lives and roughly 10 million people have been displaced, you are going to have to come to a settlement over Syria.
“That even if there may be a transitional period, ends up with a new constitution and a new government within the country because otherwise it won’t be acceptable to the people there, so if you want to exercise influence in that regard you have also got to be prepared to be committed there too.”
Asked if he was feeling the pressure to change his line on Iraq ahead of the coming Chilcot report into the Iraq war, he replied: "No I don’t feel pressure to do that.
"But I understand there is powerful disagreements about what I did…in the end you take a decision and you take it on the basis that you think it’s right, particularly when you are dealing with issues of war and peace."
The former premier also revealed that he was prepared to appear alongside Gordon Brown to help with the campaign to keep the UK in the EU.
“Well I wouldn’t object to that at all actually, and despite all the differences and difficulties, I still have a huge respect for him, and I think there is a moment when people should try and come together and it doesn’t matter whatever the other issues are that you may disagree about, this is going to be one of the biggest decisions this country has taken in the last half century.”
But Mr Blair also had a barb at Mr Brown when asked - by comedian Al Murray - if he had any advice for any prime minister dealing with “an ambitious chancellor”, a reference to Mr Cameron and Mr Osborne.
He replied his advice would be: “Probably, 'hang on in there as long as you can'.”.