Washington firmly believes that the departure of its strongest partner in Europe would also reduce American influence on the continent, as Britain so often shares American views.

An EU without Britain would be seen as weaker on free trade and less reliable on defence and foreign policy issues.

With David Cameron now saying a Britain out of Europe was now “imaginable”, US agitation has reached a new high…

“It is important to state very clearly that a strong UK in a strong Europe is in America’s national interest,” said a senior US administration official. “We recognise national states but see the EU as a force multiplier.”