The British government has announced that its legal advice says military attacks on Syria are justifiable on humanitarian grounds.

If the UN Security Council cannot agree on what to do the UK will be allowed under international law to take exceptional measures.

The British Prime Minister insisted "this is not like Iraq" as he argued the "abhorrent" attack in Damascus last week could not be ignored.

David Cameron said Britain should stand by the "international taboo" which condemns chemical weapons. And he told MPs a UN Security Council resolution should not be the only possible basis for action.

Indicating Britain would ignore a veto by Russia or China he said his test would be whether there was "overwhelming opposition at the UN".

Downing Street revealed the legal position and its intelligence advice shortly before the start of the Commons debate about the crisis.

The legal document states "The use of chemical weapons by the Syrian regime is a serious crime of international concern, as a breach of the customary international law prohibition on use of chemical weapons, and amounts to a war crime and a crime against humanity".

"However, the legal basis for military action would be humanitarian intervention; the aim is to relieve humanitarian suffering by deterring or disrupting the further use of chemical weapons."

Syria has warned British MPs to avoid 'reckless action' or face the consequences. The regime claims any such action could strengthen Al-Qaeda.

The UK has sent six RAF Typhoon jets to neighbouring Cyprus, as a 'prudent and precautionary measure'.

And Syrian leader Bashar al Assad issued a fresh warning, vowing his country would "defend itself in the face of any aggression".

Meanwhile, reports suggested Russia is sending an anti-submarine ship and missile cruiser to the Mediterranean.

Addressing the House of Commons which was recalled to discuss the Syrian situation British Prime Minister Cameron stated the legal case.

"We have a summary of the govenrment's legal position, making explicit that military action would have a clear legal basis; we have the key in dependent judgments of the Joint Intelligence Committee making clear their view of what happened and who is responsible" he said.

"And we have a motion that sets out a very careful path of steps that need to be taken before Britain could participate in any direct military action" he added.

Watch LIVE coverage below: