IS are 'not Muslims but monsters'

In an emotional statement in Downing Street after chairing a meeting of the Government's Cobra emergency committee to discuss the killing, he hailed Mr Haines as a "British hero" and vowed to "hunt down those responsible and bring them to justice no matter how long it takes."

Islamic State were "not Muslims they are monsters", he said, and the UK could not afford to ignore the severe threat the jihadists' spread posed to both world and domestic security.

The Islamic State (IS) released the footage showing the 44-year-old being murdered by a knife-wielding militant, who appears to speak with a British accent. The clip also includes a threat to kill a second British hostage.

Mr Haines was captured in Syria in March last year. In a statement his brother said the father-of-two had been murdered "in cold blood".

IS released footage late last night showing the 44-year-old being murdered by a knife-wielding militant, who appears to speak with a British accent.

The clip also includes a threat to kill a second British hostage.

Mr Cameron said the father-of-two was "murdered in the most callous and brutal way imaginable by an organisation which is the embodiment of evil".

"David Haines was a British hero. The fact that an aid worker was taken, held and brutally murdered at the hands of ISIL sums up what this organisation stands for," he said.

"They are killing and slaughtering thousands of people - Christians, Muslims, minorities across Iraq and Syria. They boast of their brutality.

"They claim to do this in the name of Islam. That is nonsense. Islam is a religion of peace. They are not Muslims, they are monsters."

He said the extremists planned to bring their terror to the streets of Britain, meaning there was "no option of keeping our heads down that would make us safe".

"We cannot just walk on by if we are to keep this country safe. We have to confront this menace. Step by step, we must drive back, dismantle and ultimately destroy ISIL and what it stands for.

"We will do so in a calm, deliberate way, but with an iron determination.

"We will not do so on our own, but with working with our allies, not just in the United States and in Europe, but also in the region.

"Because this organisation poses a massive threat to the entire Middle East. So we will defeat ISIL through a comprehensive and sustained counter-terrorism strategy."

Government sources had indicated that the death would not change Britain's policy and Parliament would not be recalled to discuss the grim development.

But Mr Cameron gave his strongest signal yet that British military involvement could be stepped up beyond supplying ammunition and training to Kurdish forces.

Backing US president Barack Obama's promise of direct American military intervention in Iraq and Syria, he said: "This is not about British combat troops on the ground, it is about working with others to extinguish this terrorist threat.

"As this strategy intensifies we are ready to take whatever steps are necessary to deal with this threat and keep our country safe."

Mr Cameron said the UK would seek to "mobilise the broadest possible support to bear down" on IS at the United Nations as efforts continue to form a coalition of countries - especially those in the region - to take part in a concerted offensive.

After some criticism of anti-terror proposals brought forward after the deaths of two US hostages apparently beheaded by the same British jihadi, he pledged to "maintain and continue to reinforce our formidable counter-terrorist effort here at home".

And he said it was vital to "drain the poison" in British society that had led some people to travel to Syria to join the extremist cause.

"People across this country will have been sickened by the fact it could have been a British citizen, a British citizen who carried out this unspeakable act. It is the very opposite of everything our country stands for," he said.

"It falls to the Government and to each and every one of us to drain this poison from our society and to take on this warped ideology that is radicalising some of our young people.

"The murder of David Haines at the hands of ISIL will not leave Britain to shirk our responsibility with our allies to deal with the threat that this organisation poses. It must strengthen our resolve.

"We must recognise it will take time to eradicate a threat like this. It will require, as I have described, action at home and abroad. This is not something we can do on our own, we have to work with the rest of the world.

"Ultimately our security as a nation, the way we go about our everyday lives in this free and tolerant society that is Britain, has always depended on our readiness to act against those who stand for hatred and who stand for destruction. That is exactly what we will do."

Mr Cameron praised the "extraordinary courage" shown by the Haines family during the long and ultimately unsuccessful efforts to secure the release of the hostage, whose "selflessness, his decency, his burning desire to help others has today cost him his life.

"The whole country, like his grieving family, can be incredibly proud of what he did and what he stood for in his humanitarian mission," he said.

In a statement issued by the Foreign Office, Mike Haines said his brother, who previously served in the RAF and worked for the UN in the Balkans, was "just another bloke" who was "most alive and enthusiastic" in his humanitarian roles and will be "missed terribly".

He said: "His joy and anticipation for the work he went to do in Syria is for myself and family the most important element of this whole sad affair."

Mr Haines had a teenage daughter in Scotland from a previous marriage and a four-year-old daughter, Athea, in Croatia with his present wife.

US President Barack Obama said America - where the two previous killed hostages, both journalists, were from - "stands shoulder to shoulder with our close friend and ally in grief and resolve".

News of Mr Haines' death came only hours after his family issued a plea to his captors to contact them.

The video begins with an interview clip of the Prime Minister and then shows Mr Haines dressed in orange overalls and kneeling down in front of a man holding a knife in what appears to be a desert location.

In a short statement to the camera, the victim states that Mr Cameron is "entirely responsible for my execution" because he "entered voluntarily into a coalition with the United States against the Islamic State"

"Unfortunately it is we the British public that in the end will pay the price for our Parliament's selfish decisions," he says.

The militant, who appears to be the same individual who featured in the previous beheading videos, says: "Playing the role of the obedient lapdog Cameron, will only drag you and your people into another bloody and unwinnable war."

Deputy Prime Minister Nick Clegg said the the murder was "barbaric" and promised the Government "will not rest until these killers face justice" and Labour leader Ed Miliband said he was "sickened" at the murder.

Among those calling for the UK to join airstrikes was former head of the army Lord Dannatt.

"Even these serial repetitions of murders being put on television screens, they must not lead our governments to conclude that this is too difficult, too dangerous and we do nothing," he told the Sky News Murnaghan programme.

"We have got to do the right thing even if it's not currently the popular thing or otherwise we will regret not taking decisive action."

He welcomed Australia's pledge to contribute 600 troops and up to 10 military aircraft to the campaign.

"I'm sure that our Government will be thinking about what more they can be doing."

Former naval chief Admiral Lord West of Spithead said the potential for a limited number of civilian casualties from air strikes "pales into insignificance compared with the barbarity of this group".

"We have a perfect right to use all means at our disposal to do something about them," he said.

Scotland's First Minister Alex Salmond convened a "resilience meeting" to discuss the implications of the "act of unspeakable barbarism" for the Scottish Government, including the need to ensure there was no backlash against the Muslim community.

He criticised the lack of a clear wider international strategy to tackle the threat of IS and insisted any action should only be taken with the approval of the United Nations.

"There is an urgent requirement to get back under collective action under the United Nations. I would urge an urgent consideration to develop a collective response to what is a threat to all humanity."

British Muslim communities reacted with outrage and disgust at the beheading.

Dr Shuja Shafi, secretary general of the Muslim Council of Britain, said: "British Muslims condemn unreservedly the murder of our fellow Briton, David Haines. Our deepest condolences, thoughts and prayers go out to the friends and family of Mr Haines."

"These extremists in Iraq and Syria claim to be acting in the name of Islam. But there is nothing in our faith that condones such behaviour.

"Muslims in Britain and around the world have condemned these people, and the arguments they use have been refuted comprehensively as being far from the religion of Islam."