Obama (3) Image: White House/Chuck Kennedy

It could take 10 years for the UK to agree a trade deal with the US if it decides to leave the European Union, US President Obama has warned.

Having already said that the UK would be at the "back of the queue" when it comes to negotiating trade deals with the US, Mr Obama said in a BBC interview: "It could be five years from now, 10 years from now before we were able to actually get something done."

The US is already in talks with the European Union over the Transatlantic Trade and Investment Partnership (TTIP) - a major bilateral trade agreement designed to boost trade between the US and EU by reducing regulatory burdens and cutting tariffs. Pro-leave campaigners have argued that the UK would be able to negotiate its own trade deals with the US and EU. But Barack Obama stressed that it would not be as easy as that: "The UK would not be able to negotiate something with the United States faster than the EU.

"We wouldn't abandon our efforts to negotiate a trade deal with our largest trading partner, the European market."

The President also warned that the UK that if it did vote to leave the EU, it would have "less influence in Europe and as a consequence, less influence globally".

Mr Obama's comments over the weekend, made during his fifth state visit to the UK as he paid tribute to the Queen on her 90th birthday, resulted in a strong backlash from 'Leave' campaigners, who criticised the US President for getting involved in a British matter. Chief Brexiteer, Mayor of London Boris Johnson, labelled Mr Obama's reasons for wanting the UK to stay within the Union as "ridiculous and weird".

But it was Mr Johnson's attack on the US President that arguably received the biggest backlash - claiming that Mr Obama may have an "ancestral dislike of the British Empire" because he is "part-Kenyan".

The President had already defended his right to have a say on the EU referendum debate on behalf of the US. Writing in The Telegraph last week, Mr Obama said "the outcome of your decision is a matter of deep interest to the United States".