Theresa May alone will decide the terms of Britain’s departure from the EU, Downing Street has said after Boris Johnson began setting out a strategy for Brexit.

Speaking in the United States, the Foreign Secretary on Thursday said that the UK will begin formal Brexit talks “early next year” and leave the EU by 2019.

In comments that will delight Conservative Eurosceptics, he said that the discussions could be wrapped up before the two-year deadline and that Britain will be able to control its borders and do a “jumbo free trade deal”.

He also suggested that countries like Australia could send more migrants to the UK in return for signing trade deals.

And he said that it is “absolute baloney” to suggest that Britain will be unable to retain access to the European single market unless it keeps free movement rules allowing all EU citizens to live and work in the UK.

However, Downing Street sources made clear that all decisions on the timing of Brexit are Mrs May’s alone.

“The decision to trigger Article 50 his hers,” the source said. “She will be doing it at a time when she believes it is in the best interest for Britain.”

The source added: “The Prime Minister’s position has not changed.”

Mrs May has repeatedly refused to set out her plans for Brexit, believing that the UK should not “put its cards on the table” before the negotiation has even started.

David Davis, the Brexit minister, was earlier this month slapped down after he suggested that Britain could leave the single market.

In his first major interview since joining Theresa May’s Cabinet, Mr Johnson said: “What we’re doing is talking to our European friends and partners now in the expectation that by the early part of next year you will see an Article 50 letter.

“We will invoke that and in that letter I’m sure we will be setting out some parameters for how we propose to take this forward.”

He added: “You invoke Article 50 in the early part of next year. You have two years to pull it off. I don’t actually think we will necessarily need to spend a full two years but let’s see how we go.”

Mr Johnson said that it is in the “overwhelming interest” of the EU to do a deal with the UK that allows it to control its borders while still having a free trade deal with the continent.

“We are going to benefit from the fantastic opportunities for greater free trade with our friends in the EU. It’s overwhelmingly in their interest to do that.

“Not only do we buy more German cars than anybody else, we drink more Italian wine than any other country in Europe, 300 million litres of Prosecco every year. They’re not going to put that at risk.

“Of course, we need a proper deal for our financial services industries. We need to sort out the question of free movement but it is all doable.”

Mr Johnson suggested that the citizens of Commonwealth countries doing free trade deals with the EU could get easier immigration access to the UK.

“When you do free trade deals with other countries around the world you may want to look at ways in which we would make it easier than it currently is for Australians who have a job they want to come to come and do that,” he said.

“Because at the moment it is more difficult for Australians than it is for anybody from Slokavia or wherever it happens to be. I personally think that’s an oddity in the way we organise things.”

And he rejected the claims made by EU leaders that Britain cannot have access to the European single market unless it accepts free movement of migrants.

“Complete baloney, absolute baloney,” he said. “The two things have nothing to do with each other and we should go for a jumbo free trade deal and take back control of our immigration policy. “

Meanwhile, a think-tank has said that the EU has more to lose than the UK over the Brexit negotiations.

Civitas said the EU has 5.8 million jobs linked to trade with the UK, while Britain has only 3.6 million jobs tied to the bloc.