The Telegraph understands the Ministry of Defence would be ready to evacuate Britons via an airlift if called upon, but is not actively preparing to do so.

Meanwhile, British nationals were told to consider escaping Lebanon while commercial airline services were still running.

A Foreign Office spokesman said: “The Foreign Secretary has chaired a meeting of Cobra this morning on the latest situation in Lebanon and to discuss ongoing preparedness work, with the risk of escalation remaining high.

“The safety of British nationals is our number one priority which is why we’re continuing to advise people to leave Lebanon now while commercial routes remain available.”

Some British nationals in the country said they had decided to remain, at least for the moment.

A British charity worker said that although his mother was worried about him, he felt he could not abandon colleagues and those he was working with on his programme.

“I felt it would somehow be wrong to cut and run at the first moment when things go wrong,” he said.

The US, Germany, France, Australia, Canada, Jordan, Italy and Turkey also warned their nationals to escape the country as soon as possible.

A number of international airlines, including Lufthansa, Air France and Delta, have suspended flights to Beirut because of security concerns.