US presidential candidate Mitt Romney will meet David Cameron and Nick Clegg later on Thursday, having met Ed Miliband this morning as he brings his campaign to Britain.
Barack Obama's Republican challenger is expected to stress his commitment to the "special relationship" as he uses the trip to raise funds and canvass support among London's large American community.
The visit is also an important opportunity for him to demonstrate his grasp of foreign affairs and ability to represent the US overseas. He is also visiting Israel and Poland as part of the same tour.
His campaign team has already been forced to distance itself from a briefing on US-UK relations after an unnamed adviser told the Daily Telegraph that he had a better understanding of the two countries' "Anglo-Saxon heritage" than Obama, who is of African-American descent. US Vice President Joe Biden called the remarks "disturbing".
The Prime Minister, who will meet Romney at Number 10, has faced questions over his willingness to have talks with an election candidate - particularly after he refused to meet Francois Hollande, the Socialist challenger and eventual victor in the French presidential election, earlier this year.
At the time, Cameron's official spokesman said the "usual procedure" was for the Prime Minister not to meet candidates in elections in foreign countries, though it is clearly not a hard and fast rule.
There could be an awkward moment for Romney and Cameron after the presidential candidate said the preparations for the Olympic Games had been "disconcerting".
Romney, who is trailing Democrat Obama by a narrow margin in the latest polls, met Miliband and former prime minister Tony Blair on Thursday morning.
Miliband, who was warmly received by Hollande during a visit to the Elysee Palace in Paris this week, said yesterday that he would "work with whoever the US elects as president".
Speaking today he said: "I welcome this meeting because I think we come from different parties and also different viewpoints on some issues, but I think it's incredibly important that leaders work together and that we respect the electorates in each of our countries."
Romney, perhaps aware his previous comments about the Games had been noticed, said he knew "the spirit of the people in this community will welcome the athletes of the world".
He added: "My experience is that this event will change the hearts of many, many people, anyone who gets the opportunity to touch the Olympics will long remember the kind of service they can provide to the people of the world and remember the heroics of the athletes themselves."
He spoke of the "common effort" to seeing greater peace and prosperity, adding: "I appreciate the work of the military of this great nation in our joint effort in Afghanistan, the people of Great Britain have sacrificed enormously in helping bring peace to that nation."
With less than four months to go until polling day in the US, Romney will use his time in London to raise money from the many wealthy Americans who live in the city.
Tickets for a reception are priced at $2,500 (£1,600) per head, and there is a dinner, where donations of between $25,000 (£16,000) and $75,000 (£48,000) are expected per guest.