Five go mad at No 10

"Inaccurate, unhelpful and inappropriate." This was the cautious response from the Labour leader's office to speculation that, if Tony Blair is elected prime minister tomorrow, the family will move out of Islington and into 10 Downing Street. But if the opinion polls are to be believed, Tony Blair is set to become Britain's youngest leader since Lord Liverpool took office in 1812; not only this, he will also be the only prime minister in living memory whose children are all of school age and living at home.

While the public has grown used to baby-boomers on the front benches, the idea of them as family men is new, aside from displays of fixed-smile unity for constituency propaganda. John Major followed tradition by leaving Norma and his then teenage son in Huntingdon when he became PM, having already spent some months away at Downing Street as Chancellor at No 11.

Tony Blair, however, has sought to identify himself as one of the pram- pushing generation. Not just a father but a dad, someone who is involved with his children, dropping them off at school, pushing their swings and, in one election broadcast, joking with them over the breakfast table. Wherever Blair goes his children, Euan aged 13, Nicholas, 11 and Kathryn, nine, must follow.

The question is, can they and should they? According to Tamsin Slyce, daughter of Peter Jay and granddaughter of James Callaghan, the childhood advantages of being related to the prime minister are scant and lie almost entirely elsewhere. "What was really nice was going to Chequers, because that had an indoor pool," she recalls. "We were allowed to peek into the Cabinet Room at Downing Street once but that was about it. I can't remember the flat at all."

It's hardly surprising. The prime minister's flat is designed as a purely functional living space, anonymous enough not to offend the incumbent resident and perfectly suited for the bachelor-style isolation most prime ministers choose. It has four bedrooms, a sitting room, dining room, kitchen and two or three bathrooms. But the building is first and foremost a government workplace and if a diary account by Harold Nicholson is anything to go by, barely hospitable. The then prime minister Ramsay Macdonald was hardly able to locate a drink and some matches for his friend in the dark, unwelcoming building. For children and a nanny used to a large house in Islington as well as Myrobella, the sprawling constituency home in Sedgefield, the converted servants' quarters would seem impossibly cramped.

Successive occupants may have attempted to make Downing Street less forbidding but it has been "home" to very few. Harold Wilson lived for a time in a government-owned property in Lord North Street, near the Commons; James Callaghan barely moved into Downing Street during his prime ministership from 1976 to 1979. There are a number of alternative government-owned residences available to the prime minister even now, in the Admiralty, in Carlton Gardens and in Belgravia. The last young people to spend much time in Downing Street were Harold Macmillan's grandchildren who stayed occasionally in school holidays from 1957 to 1963. It is almost impossible to imagine Blair's boisterous brood, whose homes, according to their father's biographers, "bear the scars" of their presence, getting used to the formality of Downing Street. Or the notoriously haughty Whitehall mandarins picking their way around roller-skates, football boots and school bags as the Blairs' house callers often have to.

Carol Thatcher was an adult by the time her mother became prime minister, and her answer to the accommodation problem is forthright. "If you're prime minister you just say: 'This isn't your office any more, it's my children's playroom'," she argues. "There are plenty of surrounding rooms and that's one of the advantages of the job."

One option might be to extend the flat, either by converting rooms currently used as computer training rooms and offices, or by knocking through a wall to the Chancellor's residence, No 11, which would probably be occupied by Gordon Brown, a bachelor who might therefore be prevailed upon to give up some space.

Should the Blairs wish to take a more conciliatory line, their only option will be clever design. Debbie Djordjevic, of Homes and Ideas magazine, advises the Blairs to consider a multi-purpose approach to the flat. "They could redesign the living room to incorporate a study," she suggests. "Platform beds are wonderful for creating more room and the children could have desks underneath where they could do their homework" - one of Blair's great political hobby-horses.

"Single bright colours are in vogue and give a sense of space - and they're washable," she adds. "Other than that, it's a tall order. Employ Swampy to tunnel into No 11 and all live together, perhaps?"

Ultimately, whether the flat is hung with paintings from the National Gallery reserve, as is traditional, or pictures of Baby Spice and Ryan Giggs, as is likely, there will be those who wonder if Downing Street is a suitable environment for anyone to grow up in. There is bound to be unwelcome attention upon them, even danger, and every slip-up and indiscretion will be used against them.

"For all the minuses there will be plenty of pluses because they can spend time at Chequers, which is lovely," says Carol Thatcher. "The flat is really just living above the shop"n