US president Barack Obama has launched a fresh intervention into the Brexit battle, warning the UK would have to wait up to a decade for a trade deal with America if it quits the EU.
Unbowed by a furious backlash from the Leave camp against his "interference" in British affairs during his visit to London, Mr Obama reinforced his stark statement that the UK would be at "the back of the queue" for a beneficial economic arrangement if it breaks away from Brussels.
"My simple point is that it's hard to negotiate trade deals. It takes a long time, and the point is 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, but rather it could be five years from now, ten years from now, before we were able to actually get something done," Mr Obama told the BBC.
Denying that he was a "lame duck" president as prominent Leave figures have alleged, Mr Obama delivered a direct slap-down to the Brexit camp who had claimed the UK could cut a speedy deal with the US.
"The point I was simply making was that for those who suggested that, you know, if we could just not be entangled with the Europeans, our special relationship is going to mean that we can just cut the line and just get a quick deal with the United States, and it will be a lot more efficient, and that's not how we think about it.
"I don't think that's how the next administration will think about it, because our preference would be to work with this large bloc of countries," Mr Obama said.
The president made it clear he believed it would be damaging for the British economy to quit the EU.
"If I am a business person or a worker in Britain, and I'm 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% of my exports, the idea that I'm 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," Mr Obama said.
The president also warned that the security of the West could be weakened by a British withdrawal which took it out of communications between Brussels and Washington.
"I think we will together be less effective if we're not in those forums, than we are currently, where we've got this great ally who engages in unmatched co-operation, with us in the room negotiating.
"You know, things as simple as making sure that passenger lists are shared, it took a lot of years for us to be able to negotiate that with the European Parliament and EU, and our strongest advocate for getting that done was the UK, and it was extremely helpful.
"What we do believe is that the United Kingdom will have less influence in Europe and as a consequence, less influence globally, and since we rely heavily on the UK as a partner globally on a whole range of issues, we'd like you to have more influence. We'd like you to be at the table, helping to influence other countries who may not oftentimes see things as clearly from our perspective as our British partners do," Mr Obama said.
Mr Obama rowed back from criticism that Prime Minister David Cameron became "distracted" after the military action in Libya as the country slipped into turmoil.
"Well, I think that we were all distracted. You know, that portion of my comments, I'm sure got attention here. What maybe got less attention was my statement that one of my regrets is not fully anticipating the degree of concentration of focus that would be required after the campaign to make sure that Gaddafi wasn't killing his own people in Libya," Mr Obama said.
The president heaped praise on his wife Michelle, saying: "I cannot separate anything that I've achieved from the partnership that I've had with that remarkable woman. So I could not be prouder of her, and I think it's fair to say that anything good that I've done, she gets a shared billing."