Gordon Brown's political nightmare will continue to haunt him today when he welcomes to Downing Street the man who is arguably the world's most popular politician.
Barack Obama arrived in London last night from Paris on his plane, nicknamed "Obama One", having conquered continental Europe and been anointed with headlines of "Obamania" in European newspapers.
After emerging from the aircraft – which has his catchphrase "Change we can believe in" printed on its side – a relaxed Mr Obama met the American ambassador, Robert Tuttle, and his wife, Maria, before greeting the waiting press. The presidential candidate and his entourage were then driven to their West End hotel, the Hyatt Regency London near Marble Arch, in a convoy of black Mercedes people carriers.
In Paris, where opinion polls mirror those across Europe by showing public support for his candidacy as US president, he appeared to have won the unofficial endorsement of President Nicolas Sarkozy, who praised him effusively at a news conference. Mr Obama and the French President emerged from talks that focused on the hot spots toured by Mr Obama on his international trip: Iran, Iraq and Afghanistan.
On Thursday, Mr Obama successfully played the political rock star in Berlin with the only public event of his global tour, when he delivered a speech to more than 200,000 Germans in the city's central Tiergarten.
Mr Brown could have bathed in the reflected glory of the Democratic presidential candidate by holding a joint press conference with him today after their scheduled 45-minute meeting. However, he is forbidden by protocol from doing this as he did not hold a press conference with John McCain, the Republican candidate, last May.
M. Sarkozy threw such diplomatic niceties to the winds yesterday, having allowed Mr McCain to answer journalists' questions alone outside the Elysée Palace during his visit. The French President, whose popularity ratings are as dismal as those of Mr Brown, clearly hoped for a "bounce" as he revelled in the presence of Mr Obama, whom he described as "my mate" in Le Figaro.
Mr Brown and Mr Obama, therefore, will be pictured in a formal "grip and grin" handshake outside No 10, before the candidate takes questions in the street.
Before meeting the Prime Minister, the Illinois Senator will have breakfast with Tony Blair, for discussions on the Middle East and global warming. They have met twice previously – in Downing Street and in Washington, when Mr Blair was prime minister and adored by the American public.
And finally, Mr Obama will go to Parliament to meet with the Tory leader, David Cameron. There again, "protocol parity" with Mr McCain will be in force, and the two men will be pictured in New Palace Yard in the Palace of Westminster.
The European leg of Mr Obama's trip, in which he has stressed the need to renew transatlantic co-operation, has played to Europeans' yearning to see the end of the Bush era.
Although the Tories are more natural soulmates with the Republicans, "Obamania" seems to have spread to Mr Cameron's party. A survey by Populus shows that 70 per cent of Tory and Labour MPs expect him to defeat Mr McCain and that almost 40 per cent of Tory MPs want him to win. But, in this febrile atmosphere, a slip of the tongue can cause problems, such as when a European diplomat recently referred to the Democratic candidate as "President Obama".
When Mr Obama noted in Berlin that his grandfather was "a cook, a domestic servant to the British", that added to the worries of Britain's ambassador to Washington, Sir Nigel Sheinwald. Whoever is elected president in November, Sir Nigel has to ensure that the "special relationship" between London and Washington flourishes. But thanks to Mr Blair's role in promoting the Iraq war and the legacy of torture in the war on terror, the omens are mixed. That is why Sir Nigel will be anxiously hovering around the corridors of No 10 today, while Mr Brown and Mr Obama hold their tête à tête.
Tight security for Obama's UK visit
Barack Obama's visit to London is private rather than official, but Scotland Yard will still provide extra security for the presidential candidate as he travels through the capital. Armed officers will be working with agents from the US Secret Service – and a police helicopter will be deployed. It is also expected that some central London streets will have temporary vehicle restrictions.
Mr Obama first requested Secret Service protection in May last year – the earliest that a presidential candidate has received the protection.
The agency, which also provides protection for the Republican contender John McCain, has asked for an extra $9.5m ($4.2m) to cover the cost of following the two candidates. They previously budgeted $106.65m for the campaign cycle, compared with $73.3m for the 2004 election.
Israeli newspaper attacked for publishing Obama prayer
*The Israeli newspaper Maariv has provoked outrage in Israel after it published the words to the prayer that Barack Obama left in a crack of the Western Wall in Jerusalem. The prayer reads: "Lord, protect my family and me. Forgive me my sins, and help me guard against pride and despair. Give me the wisdom to do what is right and just. And make me an instrument of your will."
Many visitors to the Wailing Wall, which Obama visited on Thursday, leave notes bearing requests and prayers.