James Foley beheading: Foreign Secretary rules out working with Syria's Assad regime to combat Isis after calls for alliance

The UK almost intervened in Syria last year after chemical weapons attack

Isis fighters wave flags as they take part in a military parade along the streets of Syria's northern Raqqa province (Reuters)

The Foreign Secretary has rebuffed calls for Britain to form a military alliance with the Assad regime in Syria to combat the Islamic State (Isis).

The former head of the Army and Sir Malcolm Rifkind were among those suggesting the UK could work with the Syrian President Bashar al-Assad to push back the jihadists but Philip Hammond said it would not be "practical, sensible or helpful".

"I do not think that engaging in a dialogue with the Assad regime would advance the cause that we are all advocating here," he told BBC Radio 4's World at One programme.

"One of the first things you learn in the Middle East is that my enemy's enemy is not my friend.

"We may very well find that we are aligned against a common enemy. But that does not make us friends with someone, it doesn't make us able to trust them, it doesn't make us able to work with them.

"It would poison what we are trying to achieve in separating moderate Sunni opinion from the poisonous ideology of IS if we were to align ourselves with President Assad."

Cameron previously said the international community should consider anything 'to get that man out [Assad] of the country and to have a safe transition in Syria' (AFP/Getty Images)

Lord Dannatt, the former Army Chief of General Staff, had called on the West to reconsider its relationship with the leader, who was internationally condemned for a crackdown on civil liberties during the 2011 Arab Spring.

“The Syrian dimension has got to be addressed. You cannot deal with half a problem,” he told BBC Radio 4’s Today programme.

“The old saying my 'enemy's enemy is my friend' has begun to have some resonance with our relationship with Iran.

"I think it's going to have to have some resonance with our relationship with Assad."

Britain joined the EU, US and majority of the Arab League calling for his resignation and his administration been implicated in war crimes and atrocities including a chemical weapons attack that killed hundreds of civilians near Damascus in August 2013.

David Cameron narrowly lost a crucial Commons vote on military intervention in Syria in the wake of the atrocity last year and had called for a “tough response” against al-Assad’s "illegitimate" regime.

But now the President’s army is one of the last bastions fighting against the advance of Isis in Syria, where it gained a foothold before starting its bloody sweep through northern Iraq.

The Syrian Government had been accused of turning a blind eye to the jihadists to let them fight the mainstream rebel groups it also opposes, but stepped up a campaign of air strikes against Isis headquarters in recent weeks.

Lord Dannatt said a conversation had to be held with al-Assad, whether “above the counter or below the counter”.

"If there are going to be any question of air strikes over Syria airspace it's got to be with the Assad regime's approval,” he added.

“Who actually understood that country, Syria, best - was it us, was it other people, or was it Assad himself?

"It's clearly turned out over the last two or three years to be a very diverse, very complicated country.”

Joining calls for Parliament to be recalled to discuss the escalating crisis in Iraq and Syria, Lord Dannatt said he believed more UK special forces may be needed on the ground in Iraq to train Kurdish troops.

He also suggested the “time will come” when the Government decides that British planes should carry out air strikes, rather than leaving it to the US.

Sir Malcolm, the former Foreign Secretary told World at One the Government had to be "harshly realistic".

He added: "We don't pretend we are chums of the Syrian regime - they are a ghastly regime, they are a horrid regime - but just as during the Second World War Churchill and (Franklin D.) Roosevelt swallowed hard and dealt with Stalin, with the Soviet Union, not because they had any naivety about what Stalin represented but because that was necessary in order to defeat Hitler, and history judged them right in coming to that difficult but necessary judgment.”

But Mr Hammond, who did not rule out arming Syrian rebels to help them fight Isis, said an international alliance rather than a collaboration with al-Assad was necessary.

“We are not going to do this on our own, except in terms of our strictly domestic security situation in the UK, we are going to do it as part of an international coalition,” he said.

“We are going to do it as part of an international coalition led by the United States working with the Iraqis, because the problem has to be tackled first of all in Iraq where Isil (Isis) has made its recent gains.

“We have a clear strategy that is based on a security track and a political track as well as a humanitarian track."