President Donald Trump has warned Syria and its ally Russia that missiles “will be coming” as Theresa May made preparations for Britain to join US airstrikes against the Assad regime.

The US President used his favoured medium of Twitter to announce his intentions, saying: “Get ready Russia” for missiles that would be “nice and new and ‘smart!’”

The Telegraph has learnt that Mrs May has ordered British submarines to move within missile range of Syria in readiness for strikes against the Assad regime that could begin as early as Thursday night.

The Prime Minister has recalled ministers from their Easter break to attend an emergency Cabinet meeting on Thursday afternoon at which she will discuss how Britain should respond to last Saturday’s chemical attack on Douma, Eastern Ghouta.

The Cabinet is expected to back Mrs May in joining US-led airstrikes, but Whitehall sources said there would still need to be “further conversations” with the US and France before a final decision could be taken, and that no timetable for potential airstrikes had yet been agreed.