GRUMPY Barack Obama insisted Britain is still at “the back of the queue” for a trade deal with the US – and relations could even unravel further if Brexit is bungled.

Challenged on his remarks during the EU referendum campaign, the US President said he thought Brits were wrong to back Brexit.

8 Barack Obama still says UK are 'at the back of the queue' on trade deal

8 The US president was speaking at the G20 summit Credit: AP

8 Theresa May and Barack Obama spoke alongside each other in China Credit: Reuters

Saying he had no regrets about weighing in, the American boss instead repeated the slight - saying only when the US ties up major ongoing deals with the Pacific coast states and the EU will the UK then get a look in.

The outgoing president also warned that there was a chance that the landmark voters’ decision could end up “unravelling what is already a very strong and robust economic relationship".

The US is the world’s largest investor in Britain as well as our largest export market.

Mr Obama was speaking alongside Theresa May after meeting her for the first time as Prime Minister before the start of the G20 summit in China – his last and her first.

Afterwards, Mrs May was banished to the sidelines in the leaders’ picture.

8 Theresa May stands on the sidelines at G20 summit

8 The president – who stands down in four months time – held out an olive branch to Mrs May Credit: Reuters

8 President Barack Obama insisted the USA would not punish Prime Minister Theresa May and Britain for the EU referendum result Credit: AP

The president insisted he had never suggested that the US would "punish" Britain for the landmark vote.

But he added: “It is absolutely true that I believed pre-Brexit vote and continue to believe post-Brexit vote that the World benefited enormously from the United Kingdom's participation in the EU.

“We’re going to do everything we can to make sure that the consequences of the decision don’t end up unraveling what is already a very strong and robust economic relationship that can become even stronger in the future.

“But first things first.

“And the first task is going to be figuring out what Brexit mean with respect to Europe.”

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Mr Obama’s no special favours vow came as it emerged No10 has been given a 15 page warning from Japan on what the Brexit deal must mean or their companies may pull out.

Japanese car firms such as Nissan and Honda as well as Tokyo’s banks will relocate to Europe unless they are still able to trade freely with the EU’s 27 other states, the stern document warns.

But the president – who stands down in four months time – held out an olive branch to Mrs May, dubbing her “a steadying influence during a time of transition”.

And over security cooperation, he also conceded “the bottom line” was that the US doesn’t have “a stronger partner anywhere in the world”.

Mr Obama “even as the UK pursues an orderly exit from the EU, today we reaffirm the very special relationship between the United States and United Kingdom.

“It will not simply endure but grow stronger with time.”

8 Theresa May says Britain will seize the opportunities that Brexit presents and make a success of it Credit: Getty Images

8 At a joint press conference President Barack Obama said he had no regrets about weighing in during the EU referendum campaign Credit: Getty Images

Mrs May won a promise from Mr Obama to “take forward consultations to ensure that the UK and US have the strongest possible trading relationship” after Brexit.

She added: "As we forge a new global role for the UK we can and will seize the opportunities that Brexit presents and make a success of it".

Earlier, on her arrival in China Mrs May said the worst ‘Project Fear’ predictions about the economy after Brexit have not come true.

But she added: “I won’t pretend it’s all going to be plain sailing.

“There will be some difficult times ahead.”

The PM also refused to rule out more welfare cuts in the future if the economy tanks – which would go back on a previous pledge made by former Work and Pensions Secretary Steve Crabb.

In the margins of the G20 yesterday, Mrs May also held talks with Saudi Arabia’s Deputy Crown Prince and Russian leader Vladimir Putin for the first time too – pushing him to help get aid convoys into Syria and to end the civilian bombing.

Today she will hold face to face meetings with India’s Premier Narendra Modi, Australian PM Malcolm Turnbull,Japan’s Premier Shinzo Abe, and Chinese host President Xi.

Brexit Secretary of State David Davis last night said leaving the EU was a “historic and positive moment for our nation”.

Speaking ahead of a Commons statement tomorrow, he said: “Brexit isn’t about making the best of a bad job.

“It is about seizing the huge and exciting opportunities that will flow from a new place for Britain in the world. There will be new freedoms, new opportunities, new horizons for this great country.”