The former head of the British Army General the Lord Dannatt has called on the UK and America to open up discussions about working with Syria to defeat ISIS. Lord Dannatt appeared on the BBC Today programme to say that despite the human rights record of President Assad the countries do now need to work together.

General Dannatt told BBC Radio 4: “I think whether it’s above the counter or below the counter, a conversation is going to have to be had with him.”

He continued: “Because if there’s going to be any question of airstrikes [against Islamic State] over Syrian airspace, it has got to be with the Assad regime’s approval.”

He went on to suggest that the House of Commons had been right to vote against military intervention in Syria last year but things had changed now. He also hinted that Britain had been naive to assume that the Arab Springs would lead to a more democratic region.

The former general also made clear that ISIS cannot be defeated in Iraq alone, and attacks on ISIS in Syria were vital. He said: “The Syrian dimension has to be addressed – you can’t deal with half a problem … the old saying, ‘My enemy’s enemy is my friend’, has begun to have some resonance in our relationship with Iran, and I think it is going to have to have some resonance in our relationship with Assad.”

He also feared that the rapid gains by the Islamic State meant that Britain may soon be drawn into a war in the region. This would include bombing targets in Syria, up until now America has only attacked ISIS targets in Iraq.

Dannatt is not alone in his view on Syria. Ryan Crocker, the former US ambassador to both Afghanistan and Iraq, also believes talks, and even military co-operation with the Syrians should now be considered. He said that the pressing need to stop ISIS committing widespread atrocities had to be the priority of the international community.

Chuck Hagel, the US defence secretary, also made clear that Washington is seriously considering expanding its airstrikes against ISIS over the Iraqi border into Syria. He said the White House was “exploring all options” against a regime that is now considered to the be biggest terror threat the world has ever seen.

“They are beyond just a terror group. This is beyond anything we’ve ever seen,” said Mr Hagel, noting that the organisation was extremely well funded and “sophisticated”.

ISIS is currently in control of an area of Iraq and Syria that is approximately the size of the UK. Their brutality has shocked the world, but unlike more established terrorist groups like Al-Qaeda they have proved able to run a state with some success.

Their fighters are better armed than the Kurdish Peshmerga that are now their principal opponents. ISIS have also used the spoils of war to pay their soldiers and establish a de facto capital city in Raqqa. They are supported by around 500 British nationals, many of whom are in senior roles within the regime.