The Royal Navy was on Saturday night deployed in the Persian Gulf to "take all necessary steps to protect our ships and citizens" in the wake of Donald Trump's decision to assassinate Iran's top general Qassim Soleimani.

Ben Wallace, the Defence secretary said he had ordered HMS Montrose and HMS Defender - a Type 23 frigate and a Type 45 destroyer - to accompany British-flagged ships through the Strait of Hormuz.

Mr Johnson flies back in the UK on Sunday from his holiday in Mustique facing his biggest foreign policy crisis of his premiership.

He is likely to be briefed immediately by his National Security Adviser Sir Mark Sedwill who spent Saturday locked in meetings with the heads of the UK's spying agencies, on risks to UK assets in the Middle East.

Dominic Raab will hold talks with Mike Pompeo, the US secretary of defense, in Washington on Thursday and with his counterparts from France and Germany early next week, a Foreign Office spokeswoman confirmed.