Donald Trump has said he and Boris Johnson have already started working on a free trade deal between the US and the UK.
The US president said the pair had spoken since Mr Johnson became prime minister and that they plan to spend time together to formulate an agreement.
Downing Street confirmed that talks between the two leaders had taken place on Friday evening and that they would meet at a G7 summit in Biarritz, France, next month.
Number 10 said Mr Trump had expressed his commitment to an “ambitious free trade agreement”, with formal talks to begin “as soon as possible after Britain leaves the EU”.
In another Friday night phone call, Downing Street said Canadian Prime Minister Justin Trudeau also pledged to work towards a “smooth transition” to a free trade agreement with the UK after Brexit.
Mr Johnson will be hoping it means talks towards both begin in earnest on 1 November, having pledged that Brexit will happen “do or die” on the current Halloween deadline.
Discussions over UK-US relations are likely to have begun in advance of Mr Johnson entering Number 10, as the PM had a phone call with Mr Trump before his leadership victory was confirmed.
Mr Trump said last week that he “looks forward to working” with Mr Johnson, who he has repeatedly praised in recent months, and added he was confident “he will work out Brexit”.
His praise has continued amid long-standing claims of an unwillingness on the part of the new prime minister to speak out against the president.
Earlier this month, Mr Johnson was accused of throwing the former British ambassador to the US “under a bus” for refusing to support for him during a TV debate with Jeremy Hunt.
Sir Kim Darroch resigned over leaked memos in which he described the Trump administration as “inept”, prompting an angry Twitter outburst from the president.
Mr Johnson insisted afterwards that Sir Kim had his full support and that he would “continue to be robust” with Mr Trump if he became prime minister.
He pointed to his criticism of comments made by Mr Trump in which he told four US congresswomen to “go back” to the “broken and crime infested places from which they came” as evidence of his willingness to speak out, although he declined to condemn those remarks as racist.
Mr Johnson was a more vocal critic of Mr Trump during his time as London mayor, accusing him of “stupefying ignorance” and unfit for the White House after he called for a ban on Muslims entering the US.
He also hit out at Mr Trump after he said parts of London were no-go areas, joking that the only reason he would not go to New York was the “real risk of meeting Donald Trump”.
Woody Johnson, the US ambassador to the UK. has said it is unlikely that Mr Trump will hold a grudge over any past criticism, adding: “I think they have so much more in common in terms of what they want to accomplish for the good of both of our nations.”
One nation Mr Trump does not expect to hold trade talks with anytime soon is China, as he believes its government may hold out until after the 2020 US election in the hope of negotiating with a different president.
He told reporters: “I think China would probably say: ‘Let’s wait. Let’s wait. Maybe Trump will lose and we can deal with another dope, or another stiff.'”
As for talks with France, which has announced a tax aimed at US technology companies, Mr Trump said: “They shouldn’t have done this. I told them, I said, ‘Don’t do it because if you do it, I’m going to tax your wine.'”