U.S. President Barack Obama had already made several references to what he thought Britain's standing would be as a partner if it leaves the European Union trading bloc in the June referendum and he confirmed on Saturday (April 23) that he hoped to change the minds of the anti-EU 'Vote Leave' campaign supporters.

Asked by the BBC's Huw Edwards if Obama really believed the UK would end up "at the back of the queue" when trading with the U.S. Obama smiled. He said those who believed the UK on its own could do business faster with Washington than a bloc of 27 European Union nations, the U.S.' largest trading partner, were wrong. It could take 5 to 10 years before any trade deal was signed with the UK, he said. 

"The UK would not be able to negotiate something with the United States faster," Obama said. 

"If you are interested in trade we are on the cusp of getting a trade deal done with the European Union. If I am a business person, or a worker in Britain, and I am already looking at the fact that I already have access seamlessly with a massive market, one of the wealthiest markets in the world, that accounts for 44 percent of my exports, the idea that I am going to be in a better position to export and trade by being outside of that market and not being in the room setting the rules and standards by which trade takes place I think is erroneous," he added. 

In the interview aired in full in the BBC news, Obama said he hoped to have some influence on how voters think and that he believed it would be relevant to hear what the president of the United States, who loves the British people and cares deeply about the special relationship between the UK and the U.S. had to say about it. 

"Its worth paying attention," he said.

He also said that cooperation between British and U.S. intelligence agencies would be damaged if Britain votes to leave the European Union.

"Our intelligence teams work extremely closely, our militaries work extremely closely together. That cooperation is not going to be changed."

"What we do believe is that the United Kingdom will have less influence in Europe and as a consequence, less influence globally, on a whole range of issues, we like you having more influence," he said 

Obama left Britain on Sunday bound for Germany, where he will hold talks with German Chancellor Angela Merkel, one of his closest allies in dealing with a shaky global economy and security crises in the Middle East and Ukraine.