The Union Flag flies next to the European Flag outside the European Commission building in central London

‘The US would not be keen to pursue a trade deal with Britain if it were to leave the European Union, one American official has said.It marks the first public acknowledgement by the US of a stance on the upcoming referendum.

Prime Minister David Cameron will call an in/out referendum before the end of 2017 after he has attempted to renegotiate the terms of the UK’s relationship with the EU.

But comments from US official Michael Froman made on Wednesday suggest the UK’s trade relationship with the US would be put under strain if Britain decides to leave the bloc.

The comments challenge a key pledge among those in the ‘out’ campaign, who say Britain would prosper on its own by securing free trade agreements with partners like the US.’

Read more: US official warns Britain to stay in EU or risk trade restrictions