MPs will be recalled to Parliament for a debate and vote on Syria on Thursday, David Cameron has announced.

The Prime Minister said there would be a clear Government motion laid before MPs on the UK's response to the chemical weapons attack on the outskirts of Damascus that left hundreds dead.

Mr Cameron returned to Downing Street after cutting short his summer holiday to meet Cabinet colleagues and continue talks with international leaders to find a "proportionate" response which will "deter" the Syrian state from using toxic agents.

He wrote on Twitter: "Speaker agrees my request to recall Parliament on Thurs. There'll be a clear Govt motion & vote on UK response to chemical weapons attacks."

The recall comes after Downing Street confirmed that Britain's armed forces are drawing up contingency plans for military action.

Syrian President Bashar Assad's regime has denied "utterly and completely" that it was behind the atrocity and has warned that military action would be a violation of international law and doomed to fail.

No 10 indicated that an agreement on the next steps could be taken before the results of a report by UN weapons inspectors into the attack is produced but insisted that any response would be legal.

"No decision has yet been taken," a Downing Street spokesman said. "We are continuing to discuss with our international partners what the right response should be, but, as part of this, we are making contingency plans for the armed forces."

Cabinet ministers, including Defence Secretary Philip Hammond, have arrived at No 10 for talks ahead of a national security council (NSC) which will discuss possible UK involvement in using force.

Foreign Secretary William Hague has cancelled plans to meet Swedish foreign minister Carl Bildt in Stockholm tomorrow in light of developments in Syria and the decision to recall Parliament, the Foreign Office confirmed.