Marco Rubio, the bookmakers’ favourite to be the Republican presidential nominee, has said that Britain could leave the European Union and still expect the special relationship with the US to flourish.

The Florida senator’s tacit blessing for a British exit is in sharp contrast with President Obama’s staunch opposition to it and reflects growing Republican scepticism towards the EU project.

“Irrespective of what decision the UK makes . . . they’ll continue to be certainly our best friend in the world and one of our strongest alliances,” Mr Rubio told The Times.

Speaking at a gathering of US chief executives organised by The Wall Street Journal, Mr Rubio said: “Part of us being a strong ally [of Britain] is for us to respect