Donald Trump's pledge to work to secure a rapid trade agreement with Britain after Brexit is "very good news", Boris Johnson has said.
The Foreign Secretary said a deal could be "very much in the interests of both sides" after the US president-elect made clear it would be a priority for his administration.
In an interview with The Times and German newspaper Bild, Mr Trump said he would be inviting Theresa May for early talks in Washington following his inauguration on Friday and predicted leaving the European Union would be a "great thing" for the UK.
In contrast to Barack Obama, who said Britain would be at the "back of the queue" when it came to a trade deal with the US, Mr Trump made clear it could be done "very quickly".
"We're going to work very hard to get it done quickly and done properly. Good for both sides," he said.
"I will be meeting with (Mrs May). She's requesting a meeting and we'll have a meeting right after I get into the White House. I think we're going to get something done very quickly."
Mr Johnson and Downing Street welcomed Mr Trump's comments, which came in an interview with former Cabinet minister Michael Gove.
Speaking at a meeting of EU foreign ministers in Brussels, Mr Johnson said: "I think it's very good news that the United States of America wants to do a good free-trade deal with us and wants to do it very fast.
"It's great to hear that from president-elect Donald Trump. Clearly it will have to be a deal that's very much in the interests of both sides, but I have no doubt that it will be."
Mrs May's official spokeswoman said the intervention " highlights one of the opportunities of the UK leaving the EU".
The spokeswoman said Mrs May's expected visit to Washington in the spring would provide an opportunity for "early discussions" on a UK-US trade deal, but stressed Britain will respect EU rules which bar it from signing agreements with third parties so long as it remains a member.
The spokeswoman said it would be possible to hold "scoping discussions" before Brexit takes place on possible measures to bring down barriers to UK-US trade.
"We welcome the enthusiasm and energy the president-elect and his team are showing for engaging with the UK," she said.
Mr Gove said he understood Mr Trump wanted a "signature-ready" deal on the table "at the earliest possible opportunity".
Speaking to Mr Gove, the co-leader of the Leave campaign, Mr Trump also made clear, unlike Mr Obama, he welcomed the result of last June's EU referendum vote.
"People, countries want their own identity and the UK wanted its own identity. Brexit is going to end up being a great thing," he said.
In a wide-ranging interview, Mr Trump disclosed:
:: He wants a new arms control agreement with Russia, saying the number of nuclear weapons should be "reduced very substantially";
:: Orders will be signed next Monday strengthening America's borders which could include travel restrictions on Europeans coming to the US as well as "extreme vetting" of those entering from parts of the world known for Islamist terrorism;
:: He believes Chancellor Angela Merkel made a "catastrophic mistake" when she threw open Germany's borders to hundreds of thousands of migrants.
In his first UK interview since becoming president-elect, Mr Trump identified the refugee crisis as one of the key factors driving the Brexit vote.
"I do believe this, if they (EU countries) hadn't been forced to take in all of the refugees, so many, with all the problems that it ... entails, I think that you wouldn't have a Brexit," he said.
"It probably could have worked out but this was the final straw, this was the final straw that broke the camel's back."
Mr Trump spoke warmly of how he was looking forward to visiting Britain, saying his Scottish mother was "so proud of the Queen".
"Any time the Queen was on television, an event, my mother would be watching," he said.
He joked his Scottish ancestry meant he liked to "watch my pennies", adding: "I mean I deal in big pennies, that's the problem."
Mrs May's spokeswoman confirmed the PM sent Mr Trump a Christmas gift of a copy of Winston Churchill's address following the Japanese attack on Pearl Harbour, in which he expressed his hope the British and American people would "walk together in majesty, in justice and in peace".
In a letter, she said she hoped the feeling of "unity and fraternal association" between the two countries was "as true today as it has ever been".
The Prime Minister's spokeswoman said it appeared Mr Trump was "delighted" with the gift - sent a few days after Christmas - but indicated that he had not sent Mrs May anything in return.
She dismissed suggestions Mrs May might be concerned that Mr Gove - now a backbench MP working as a £150,000-a-year columnist for the Times - had met the president-elect before her.