Donald Trump has said talks about a “very substantial” trade deal with the UK are under way.
A bilateral deal with post-Brexit Britain could lead to a “three to four, five times” increase in current trade, the US president said.
After a phone call with Boris Johnson on Friday, the US president said the new prime minister would be “great”.
No 10 said both leaders used the phone call to express commitment to delivering an “ambitious” trade deal.
Mr Johnson and Mr Trump said they would begin negotiations “as soon as possible” after the UK leaves the EU, Downing Street said.
The phone conversation comes after the American ambassador to the UK, Woody Johnson, said relations between the US and UK would be “sensational” now Mr Johnson was in Downing Street.
A supporter of Brexit, Mr Trump was critical of Theresa May’s negotiations with the EU. He welcomed Mr Johnson’s rise to power, even suggesting he was a “British Trump”.
As a member of the EU, the UK is part of about 40 trade agreements the EU has with more than 70 countries. The EU does not have a trade agreement with the US.