Had the prime minister not faced perhaps his least comfortable interview with Newsnight's Jeremy Paxman on the fallout from the Labour mayor contest just hours before, the baby-sceptics asked.

Could the announcement be timed to distract attention from the embarrassing saga leading to Ken Livingstone's inclusion on the shortlist for the job, they wondered.

But it took a brave cynic to voice such doubts in public amid the massive interest in Cherie Blair's pregnancy and the chorus of congratulations.

Among the first to do so was Steven Norris, the former transport minister who lost out to Lord Archer in the contest to become the Conservative candidate for London mayor.

"My instant reaction was, I must say, hey, that is brilliant timing, that is really Alastair Campbell, (the prime minister's official spokesman) at his best," he said.

"That does make cynics of us all, doesn't it, and I'm afraid it doesn't do a lot for the political process because if that's the way our politics is being packaged these days, I think we are all the poorer for it," he told Talk Radio.

Tory MP Roger Gale added his doubts: "It does seem rather as though there is absolutely nothing that this presidential-style prime minister is not prepared to allow his spin doctors to exploit for party-political purposes and that is very sad.

"Some will inevitably feel that for the sake of one day's headlines, presumably designed to limit Ken Livingstone's front-page space, Mr Blair's news managers have rather diminished a personal and happy occasion."

But for those who would rather believe that some things should always remain beyond the spin doctors, publicist Max Clifford offered an account of how he helped Mirror editor Piers Morgan break the story without political interference or direction.

He said a source "very close" to the family but in no way political had tipped him off on Monday about the pregnancy.

When The Mirror editor then contacted him saying he had heard a similar rumour and could the PR supremo confirm it he agreed he could.

"I was 100% certain it's true and that they had told the children," he said.

He refused to name his contact. "It was from somebody who is very close to the Blairs but they're not a political person and that's all I'm prepared to say.

"All I know is that it was someone very close to them and who was very happy."

The Mirror editor, also speaking on Talk Radio, hit out at the cynics and snipers.

"The first reaction of Downing Street was to give a huge groan and say if they did this today then everyone is going to think they've only done it to keep Ken Livingstone off the front page," he said.