Britain’s military chiefs have drawn up contingency plans to provide Syrian rebels with maritime, and possibly air, power in response to a request from David Cameron, senior defence sources said on Monday night.

However, they said the UK would act only if the US did so and made it clear that British chiefs of staffs are seriously worried about the consequences of intervening in the Syrian crisis.

Military sources have privately been expressing growing concern about pressure from Downing Street.

Officials compared it to the pressure applied by Cameron before Britain and France took the lead in the campaign of air strikes on Libya early last year.