f Cherie Blair hadn't got morning sickness already, the papers might just have brought it on. Blooming Cherie clutching a tabloid's bouquet, pages and pages of baby bliss, fashion advice for mothers-to-be ... everything bar a cut-out-and-keep guide to making your very own Blair babe.

So the Prime Minister and his wife are having a fourth child. Brilliant. Good for them. It is a wonderful story and a real coup for the newspaper that broke it. But by day two, coverage was spiralling out of control as rival editors compared their scoop sizes. Worse still, the media frenzy was being fuelled by Alastair Campbell, the Prime Minister's press secretary, who was only too happy after seeing the Ken Livingstone fiasco on every front page for a week to feed everyone a few titbits, including a less than subtle hint about where and when the child was conceived.

Poor Mrs Blair. She wasn't even allowed the luxury of telling her own father he was going to be a grandfather again, or get used to the idea of being pregnant at 45. Then there was the inevitable row over who had got the story first.

The Sun claimed it as a "world exclusive", arguing that no one could claim the scoop as it appeared in the first edition of more than one paper. The Mirror claimed it had got the "scoop of the year", which soon became the "scoop of the millennium". Downing Street gave it the credit in the official statement confirming the story.

The story also redressed the balance between the Mirror and the Sun, its arch-rival. Earlier in the week, Rupert Murdoch's tabloid displayed a picture of the Prime Minister at its Wapping offices, marking the paper's 30th anniversary. Just to push the point home, the headline had the Prime Minister saying of the red-top: "Oooh, you are awful, but I like you." If that stuck in the craw of the Mirror's editor, Piers Morgan, his Cherie scoop must have brought a renewed smile to his face.

Getting the pregnancy story to stand up proved testing for Mr Morgan until Monday, when the publicist Max Clifford called him and said Mrs Blair had found out she was pregnant five weeks ago and that the children had been told.

Mr Morgan waited until 1pm on Thursday before contacting Downing Street, where the Prime Minister and Mr Campbell protected the Mirror's story for as long as they could. The Prime Minister even telephoned Mr Morgan to let him know Mrs Blair had been called by the Sun and that she had no choice but to tell them the truth. But that did not dent Mr Morgan's delight at getting his scoop. "It's great. We sold buckets of papers and the Sun have made themselves look vaguely ridiculous."

Once the story was out, the information flowed freely from No 10. It is highly unusual for the private lives of politicians to be aired in such a public way with the consent and co-operation of their press minders.

Mr Blair's spokesman told journalists exactly how pregnant Mrs Blair was and, denying original reports that the baby was a product of the couple's Tuscan holiday, said they could "work out" where the deed was done. We now know that Mr Blair intends to be at the birth, that it will be at an NHS hospital, that the baby will sleep in the same room as its parents in Downing Street, that the Queen knew before Mrs Blair's father, that the Prime Minister will help with nappy-changing and that Mr Blair is worried about the couple's age. "We are quite old to have a baby" he said yesterday.

But when the fuss dies down, Mr Blair's spokesman has made it clear there will be no unscheduled pictures of the children, no hordes of photographers at the hospital, no daily update of how she's doing. He insisted the "lack of intrusiveness" must continue.