Barack Obama's visit to Britain is partly motivated by a desire to improve "cooling" relations with David Cameron, it has been claimed.
Brian Donohoe, secretary of the influential British-American parliamentary group whose members include Nick Clegg, William Hague and Mr Cameron, said Foreign Office staff had been working on "overdrive" to improve relations.
"There's been a cooling of the relationship as a result of the personalities perhaps not being close to each other, between our prime minister and the president," he told politics.co.uk.
The Labour MP said he believed there was recognition of the fact that "this is something which has to be resolved" among Foreign Office officials.
"They are working in the Foreign Office on overdrive trying to square that now," he added.
"Alastair Burt is bending over himself to improve the relationship. It's part of the reason we've got this visit."
The two leaders went out of their way to appear unified ahead of President Obama's state visit, writing a joint article for the Times expressing their "perfect alignment".
It read: "[The UK-US relationship] is founded on a deep emotional connection, by sentiment and ties of people and culture. But the reason it thrives, the reason why this is such a natural partnership, is because it advances our common interests and shared values.
"It is a perfect alignment of what we both need and what we both believe. And the reason it remains strong is because it delivers time and again."
Downing Street insists Mr Cameron continues to get on well with the president. The pair have held telephone conversations around 25 times since Mr Cameron entered No 10 last year.
"It's as strong as it ever has been," a No 10 spokesperson said.
But concerns have shrouded the pair's private talks as officials privately worry about how well they get on. Mr Obama reportedly emerged from a meeting with Mr Cameron in July 2009 with the words: "What a lightweight."
They resorted to alcohol in June 2010, exchanging bottles of beer to watch the England v USA fixture on the sidelines of a G20 summit.
"I advised him that in America we drink our beer cold, so he has to put this in the refrigerator before he drinks it," Mr Obama commented at the time.
Others cite Mr Obama background and his 'Pacific' approach to international affairs as reasons for the apparent cool-off in US-UK relations.
Xavier Domandy, of foreign affairs thinktank Chatham House, said Mr Cameron and Mr Obama had a "robust and substantive relationship".
"Whether it has the same joie de vivre of Tony Blair and George Bush, which frankly raised a number of eyebrows, I think probably not," she said.
"It's certainly not President Obama's style. I think Obama's relationship with Cameron is actually a good one - substantive and developing."
She said the visit would serve as a key opportunity to discuss issues including the Arab Spring in the Middle East, Pakistan and Afghanistan and the global economy.
"Perhaps more important is engaging substantively and strategically together in advance of international meetings to ensure that both sides are together, aligned, and supporting one another," Ms Dormandy added.
The G8 summit takes place later this week, giving Britain and the US time to prepare a united front as they meet with other economic powers including China and Russia.
"What is the value of the special relationship? It's the ability of these two to bring their leverage, power and influence to bear on the broader international community."
Similar goals but different capabilities means tensions will continue, however. Britain's determination to withdraw troops from Afghanistan by 2015 could cause tensions, while the ongoing military action in Libya could prompt disagreements.
"It's clear there have been problems, particularly on the whole question of defence issues," Mr Donohoe added. He said the situation in Afghanistan and Libya would be particularly contentious.
Ms Dormandy acknowledged Libya could be a "difficult discussion".
"There's a bigger question which Libya has highlighted - that the UK needs America's engagement, both in moral terms but also in capabilities," she said.