MPs' committee says Cameron has failed to justify Syria strikes

British Prime Minister David Cameron's attempts to build consensus for air strikes against the Islamic State (IS) group in Syria have suffered a blow after a committee of MPs voted that he had failed to justify the strikes.

The cross-party Foreign Affairs Committee voted on Tuesday by four to three in favour of a motion that the British prime minister "has not adequately addressed concerns".

The vote is a blow to Cameron on the eve of a Commons vote set for Wednesday, called after opposition leader Jeremy Corbyn gave his MPs a free vote following widespread dissent against his opposition to military action.

Cameron last week made his case for military action in a response to a critical report from the Foreign Affairs Committee, setting out what he claimed was a "comprehensive" approach to the crisis in Syria.

The committee's Conservative chairman Crispin Blunt had said Cameron had gone far enough and indicated that he would support military action.

However on Tuesday night committee members Concervative MPs John Baron and Andrew Rosindell, Labour's Yasmin Qureshi and Stephen Gethins of the Scottish Nationalist Party (SNP) voted to state their misgivings.

Conservatives Adam Holloway, Daniel Kawczynski and Nadhim Zahawi backed the PM.

The vote came amid disagreements over the prime minister's claim that there were 70,000 "Syrian opposition fighters on the ground who do not belong to extremist groups," a major part of his strategy for defeating IS.

Lt Gen Gordon Messenger, the deputy chief of defence staff, told the Defence Select Committee on Tuesday that national security prevented him from saying they were members of Islamic Front and Ahrar al-Sham, two groups fighting to instate Islamic law in Syria.

Messenger told the committee: "I can’t get into detail because of the level of classification of this briefing. What I can say is there is a spectrum of extremism."

Interrupting Messenger, Lewis said: "I’m sorry, General, I don’t accept that at all. These groups are known to exist and the prime minister has come forward with a figure of 70,000 and he has obviously got a basis for that figure. There is nothing of a sensitive or classified nature about which of these known groups he is including in his total and which he isn’t.

Louise Haigh, a Labour opponent of air strikes, had earlier said that she was told by a national security adviser that the politics of more than 40 percent of that figure were of questionable origins.

Thousands march against bombing

Also on Tuesday, thousands of protesters gathered in central London in an effort to stop Britain from joining air strikes in Syria.

A crowd of around 4,000 marched from the Houses of Parliament in Westminster to the headquarters of the ruling Conservative party and main opposition Labour party nearby.

"We're here to say one simple thing, don't bomb Syria. Don't do what you did in 2001, 2003 and 2011," the Stop the War Coalition protest movement's Lindsey German told the crowd, referring to British involvement in wars in Afghanistan, Iraq and Libya.

"Don't go and bomb a country [and] make the war even worse."

Parliament looks set to vote in favour of joining the bombing campaign against IS on Wednesday, paving the way for sorties by British jets to start within days.