The largest US air and naval strike force since the 2003 Iraq war was heading towards Syria last night as Theresa May won the backing of the cabinet to join in military action.

US-led strikes after the suspected chemical weapon attack in Douma, which left as many as 40 people dead, are expected within the next three days.

The prime minister continued yesterday to face down demands for a Commons vote on whether Britain should join the US in any punitive action against President Assad.

Senior ministers decided it “was vital that the use of chemical weapons did not go unchallenged”, according to the official read-out from an emergency meeting of the cabinet yesterday. It added that they “agreed on the need to take action…