The guestlist could have included any of Mr Blair's three most senior colleagues: Robin Cook, the shadow Foreign Secretary, Gordon Brown, the shadow Chancellor or John Prescott, the deputy leader. And, as Labour MPs know, tension among the three has never been higher.
One highly-placed source concedes with understatement: "I am not going to pretend to you that any of them go on holiday together." A Labour MP put it more bluntly: "Cook, Brown and Prescott, can't stand being in the same room together." Fortunate, perhaps, that only Mr Cook will be accompanying Mr Blair to the American ambassador's London residence.
Last week in a Commons debate the Chancellor Kenneth Clarke sought to exploit the semi-public row between Mr Brown and Mr Cook. The two Scottish Labour MPs were never friends; now many see them as enemies. Both clever, both loners, there is, said one MP last week, an "almost chemical frisson" between the two which has developed over a 20-year rivalry. Brownites regard Mr Cook as "poisonous"; "never trust a man who once went on holiday to a library," retort backers of the shadow Foreign Secretary.
The latest dispute erupted over Mr Brown's plans to remove some benefit from the young unemployed who refuse a job or training. The principle had been trailed in a policy document published in October, but the detail infuriated some on the left. Mr Cook's reservations reached one newspaper front page.
Then, a week later, reports emerged of a brisk exchange at Shadow Cabinet between Messrs Cook and Brown. Mr Blair ordered a news blackout which was broken within days. Several members of the Shadow Cabinet felt the consultation processes had broken down. Critics of Mr Brown were said to include Chris Smith, Mo Mowlam and Frank Dobson.
Last week, at a meeting of the Parliamentary Party, MPs banged their desks in support of the shadow Chancellor, and later that day at a meeting of the Shadow Cabinet the Labour leader backed Mr Brown "101 per cent". He warned that if he found out who was leaking to newspapers they would have no place in a Blair Cabinet.
One source, who was careful not to blame Mr Cook, argued: "There has been an attempt to drive a wedge between Tony and Gordon and that has failed. In a way Gordon's position has been strengthened."
The enmity goes back to Edinburgh University where Mr Cook first met his younger challenger. Then, at least, there was an ideological meeting of minds. The Scotsman last week disinterred a 20-year-old copy of the Red Paper on Scotland - stated objective the pursuit of "vigorous socialist policies" - edited by Mr Brown with a contribution from Mr Cook.
The road from there to Mr Blair's revisionist Shadow Cabinet has been a long one, and it has shown up their differences. Mr Brown has become central to the modernising process.
Mr Cook, although he covets Mr Brown's economic portfolio, has devoted much of his energy to the constitutional agenda. He has championed proportional representation and expressed an interest in serving in a Scottish Parliament. His admirers see him as a potential first Scottish prime minister.
Mr Brown has been bolstered by an effective team campaign which exposed the Tories' record on tax, helped inflict a defeat on the Government over VAT on fuel and made hay over fat-cats in the privatised utilities. But this has produced complaints that Mr Brown has trampled on other people's territory and built a group of dedicated supporters around him. His chairmanship of the day-to-day news management strategy committee, and of a new weekly campaign meeting (attended by Mr Blair and members of his private office but not Mr Cook) makes friction with colleagues inevitable.
Mr Cook, who is chairman of Labour's policy forum, and is also supposed to be in charge of policy development, feels he should be consulted more. But the policy forum, a talking-shop devised by Neil Kinnock to circumvent the potentially-troublesome party conference, is something of a dead duck these days because the party at large shares the leader's consuming passion to win. And Brown's aides insist that the shadow Chancellor "will not be deflected by back-biting" from his central task of shaping an economic policy to transform Britain.
Mr Cook does not have a similar degree of support in the PLP to Mr Brown's. Nor does he have such a close relationship with Mr Blair. Last year he made it clear that he did not wish to be moved from the Trade and Industry portfolio - only to be shuffled to Foreign Affairs. His influence on economic policy is limited. Yet he retains a key and powerful job. His access to the Labour leader remains good and he is one of the handful of MPs which regularly rings Mr Blair at home. And there are signs of improving relations between Mr Cook and Mr Prescott who have never been soulmates.
The deputy leader did not play a central role in the recent dispute, although his relations with Mr Brown are famously bad. Having helped to deliver Clause IV's re-write for Mr Blair he has been sensitive about his exclusion from the leader's magic circle.
Earlier this year a row erupted when he was not invited to a private strategy meeting of Mr Blair's closest political advisers. Any further slights could prove dangerous for the leadership.
Do the tensions matter and will the Tories be able to exploit them in the run-up to the next election? True, the rows are more personal than political.But Mr Blair is concerned that the impression of disunity which arose in the summer could damage the party's public image. His backers also concede that some criticism of Mr Brown from the left (though not from Mr Cook) is a veiled attack on the leader himself.
Messrs Brown, Cook and Prescott all get on with Mr Blair. The four meet before each Shadow Cabinet without misadventure.
One MP said; "The Cook/Brown spats have a ritualistic air. They know how to get to that point just before they throw the furniture at each other - and stop." But Mr Blair might be wise to nail the tables in the Shadow Cabinet room to the floor, just in case.Reuse content