Media playback is unsupported on your device Media caption Abu Dujana: "I am prepared to die for this cause"

The West's attempts to defeat the Islamic State group in Syria depend, the UK government says, on the help of 70,000 so-called "moderate fighters" on the ground. But who are they? And who are they really loyal to?

It was said with a laugh.

Sitting in Syria, and speaking via the internet, "Abu Dujana" told me: "I'm not a big fan of the suicide attack or exploding oneself."

But after giving it careful consideration, the British Muslim convert said he was prepared to be martyred, to kill himself for his cause.

"If there is absolutely no other way - and I'm speaking from an Islamic perspective in terms of suicide attacks - it is only permissible to blow yourself up if there is no other way to overcome the enemy," he said.

He compares such a drastic step to a soldier, overwhelmed by the enemy, who pulls a pin on a grenade in order to take out as many of them as possible.

Image caption Abu Dujana says he has received military training and likens himself to the Kurdish Peshmerga fighting IS in Iraq

He is perhaps in his mid-20s, has been fighting in Syria with the Islamic Front for the past three years, and comes from "somewhere' in England.

He came, he says, with the intention of giving humanitarian help, but soon picked up a gun. His identity is hidden, the biographical details are scarce, because he realises that by killing in Syria, he risks arrest at home.

Yet, still, he could be the British government's ally on the battlefield against the so-called Islamic State group.

Prime Minister David Cameron believes there are 70,000 "moderate" rebels fighting in Syria - a figure that many believe is an overestimate - ready to face IS, also known as Isis, Isil or Daesh.

Abu Dujana is one of those moderate rebels. He meets Britain's "moderate" criteria on two points: first, that he's prepared renounce terrorism, and second, that he will accept a post-conflict Syria that includes all faiths and religions.

"We are looking to make Syria an Islamic Syria in the future, a truly Islamic Syria. The Islam that ruled at the times after the Prophet…" he said.

"If you look at history you will see that, not just Muslims, but all sorts of Muslims, Christians and Jews flourished at that time living under those rules - living under true equality and justice."

Are there really 70,000 'moderates' in Syria?

Syria air strikes: What you need to know

David Cameron admits it is too much to ask for "ideal partners" in the fight in Syria, and has asked: "Do we wait for perfection?"

Abu Dujana sees fighting in Syria as his religious duty - jihad - but says he's no different from other British citizens who have gone to fight IS and that he should be treated the same.

"What we need to look at... in terms of the Peshmerga, or the Kurdish groups that were fighting Isis, there were British and American soldiers that went to fight against Isis as well - and I'm doing the same thing.

"I've taken military training as well," he told me.

More than 700 Britons have gone to Syria to fight, mostly with IS, but no-one knows how many have taken up arms with other groups.

Britain's security services warn that friends on the battlefield may still be enemies at home, and those that have gone to fight for religious reasons are prone to radicalisation.

Media playback is unsupported on your device Media caption DAC Helen Ball: "Potentially there could be a very grave risk"

British counter-terrorism chief Deputy Assistant Commissioner Helen Ball, from the Metropolitan Police, says those who travel to Syria can quickly get lost and fall into the hands of radical groups.

"It's a place where terrible atrocities have been committed - dreadful crimes have been committed - and they're not only in personal danger, but they're also in danger of being drawn into things they actually don't agree with," she says.

The priority is finding those who have joined IS - but those with other motives are also potential targets for arrest.

"Certainly, we would put a great deal of resource into people who we are fairly sure are wanting to join Isil - that is an obviously dangerous, murderous organisation that someone wanting to join would be a real threat," DAC Ball says.

"But until we have been able to establish the facts in each case, we would put resources into every case."

Russian airstrikes and increased pressure from Syrian President Bashar al-Assad's forces have meant hard fighting for Abu Dujana recently. The front lines, he says, are "hot", but he's still been in regular touch with his family in Britain.

"I do speak to them. I try to keep things as normal as possible. So you know, I'm in a war, yes, and I have been battle-hardened if you want to say that.

"At the same time, I'm still the same… I'm still their son."