The timing couldn't be better. A new baby for the new millennium and with the elections for the mayor of London and a general election just around the corner. Even Ken Livingstone, the thorn in New Labour's side, is in danger of being overshadowed. And amid all the congratulations from political friends and opponents, the inevitable comparisons with the Kennedy Camelot dynasty.

For not only will the Blairs' fourth child, expected in May, be the first new baby at Downing Street since Lord Russell became a new father at the age of 55 in 1848, the new addition will enhance Tony Blair's reputation as a family man with the voters just as it did for President Kennedy in the 1960s.

The British press is falling over itself about the news, speculating about the timing of the conception - probably while they were on holiday in Italy this summer - and the attendant upheaval of family life at Downing Street.

But most observers agree that quite apart from the genuine surprise surrounding the arrival of a new baby - Tony Blair is reported as being "completely, totally, 100 per cent stunned" by the news - the Blairs are blazing the trail for successful "have it all" couples approaching middle age.

Their first child, Euan, was born in 1984, Nicky was born one year later and the their third child, Kathryn, is 11 years old. Few people will forget the television pictures of the new Prime Minister and his wife standing outside No 10 in May 1997 basking in the glow of election victory with their three children. The image was part of the New Labour strategy to portray the leader as a committed family man, more than capable of understanding Middle England's attempt to juggle a successful career with the demands of young children.

Tony and Cherie have had highly successful careers while raising their children just as the couples of Middle England have done. In the early days of their marriage, while Cherie was busy fighting battles in court, Tony Blair was often found changing the nappies and cooking the dinner at home in their £500,000 house in Islington after spending the day at the Commons. He may not have as much time or energy at 46 to do that now, but he has made some tantalising comments recently about his wish to spend more time with his family that further endeared him to the busy families at the heart of New Labour's electorate.

ONLY last week he confessed on BBC Radio 5 Live that if he had the choice he would much rather have stayed at home with Cherie and the children than go to South Africa for the Commonwealth Heads of Government summit. Few people would have begrudged him that after a year that saw his personal commitment to achieving peace in Northern Ireland and Kosovo take up an enormous amount of his time and energy. Among the electorate, there is no doubt that a new baby will enhance his image at a time when opinion polls have picked up on voter unease at the perception of a growing sense of arrogance and aloofness at the heart of the leadership. The honesty with which the Blairs admitted that this baby was a complete surprise and the idea of Tony Blair being kept awake by a new baby like any other father will probably check that perception of arrogance.

Cherie Booth, we should remember, was criticised this week for complaining that she couldn't afford to spend vast sums of money on new dresses to wear at the banquets and receptions she attends in her role as the Prime Minister's wife. That faux pas will soon be forgotten. Fashion advice will be replaced with tips on dealing with an unexpected pregnancy at the age of 45.

Most women in Britain are now delaying having children until they have reached their early 30s. Career comes first with the 1990s woman and most women are now deciding when to have children rather than leaving it to chance. But just in case Cherie was worried about it, the British press has already wheeled out the model Jerry Hall and the actresses Susan Sarandon and Jane Seymour, all of whom had children in their forties, as evidence that she is about to join the popular older mothers' club.

There have been a few grumbles. The former Conservative transport minister, Steven Norris, said: "My instant reaction was, I must say, hey, that is brilliant timing, that is really Alastair Campbell at his best."

One Tory MP, George Gale, said: "It seems 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 frontpage space, Mr Blair's news managers have rather diminished a personal and happy occasion."

Mr Campbell, Mr Blair's spokesman countered: "Mr Gale's remarks are ill-founded, offensive and thoroughly in character."

But apart from these, the next question on everyone's lips is: when will William Hague and Ffion deliver the first Tory babe?