Proof of the fickleness of being fashionable is the very fact that Wayne Hemingway himself may not qualify for an invite to a truly hip Downing Street soiree. Having raised the subject of hipness, the designer could have automatically disqualified himself. It has made him seem more of a Jeff Banks (very Eighties), particularly with his penchant for courting random publicity.
Rather than Hemingway, Stella McCartney, newly appointed to Chloe, and "barrow boy" Alexander McQueen should appear on Blair's list. And if the Prime Minister wants to invite the real cutting edge of British design he should try Hussein Chalayan and Antonio Berardi, tickets to whose shows were red hot this year. Berardi refused his Newcomer of the Year award at the British Fashion Awards after a mix-up during the presentation ceremony when his gong was accidentally given to someone else.
Knowing that designers usually like to trail a model or two along with them, Blair will want to invite some of the beautiful people. But he should use a bit more imagination than plumping for obvious choices Kate Moss and Naomi Campbell. He may like to dash an invitation round to Karen Elson - the 18-year-old Oldham model currently working for Chanel, Versace and Lacroix. With nine A and B grades at GCSE, Karen could even hold her own in a conversation with Cherie.
As any 14-year-old knows (if only Blair had consulted his son Euan) - Oasis's star is fading. The Verve are obvious replacements for the Gallagher brothers, but Blair can't afford to look as though he is jumping on the bandwagon. Instead of Liam and Noel, the Prime Minister could try Ian Brown, formally of the Stone Roses, who is on the crest of a much-heralded comeback. Cornershop, currently supporting Oasis on tour in America (how ironic) would be another good choice. And as Kathryn will tell her daddy, newcomers All Saints are now out-powering the Spice Girls.
If Blair wants to play the popularity card he could invite Louis de Bernieres, author of Captain Corelli's Mandoline - a book so many people read on public transport that it ought to come free with a bus pass. But if he's going to do that he may just as well ask Helen Fielding, the creator of Bridget Jones's Diary, which really wouldn't be remotely cool. Instead Blair could invite Rupert Thomson, whose new novel, Soft, all about advertising, is going to be big, big, big. Blair would also enjoy the company of TS Eliot Prize winner Dom Paterson, the poet. Paterson plays folk jazz guitar to professional standard and, as Blair has already chosen his guitar as his desert island luxury, they would have plenty to talk about.
In the art world, Damien Hirst is still just about cool enough, and Blair ought to ask him to bring along his very cool dealer, Jay Jopling, who runs the White Cube Gallery. Gillian Wearing, winner of the Turner prize, would be a hip guest, and if Blair wants some real fun he should also invite the rest of the all-female Turner short list, as well as Tracey Emin (she of getting drunk live on TV fame), although John Windsor, The Independent's art correspondent warned: "They would tear Number 10 apart."
No Downing Street bash would be complete without luvvies from the film world, but here Blair has to be careful. It would be oh so easy to go for current megastars Robert Carlyle (The Full Monty, Trainspotting) and Kate Winslet (Titanic, Sense and Sensibility), and miss out on real street cred. Ray Winston, who played alongside Kathy Burke as the scary wife- beater in Nil By Mouth, is a much less conservative option. And how much cooler is it possible to get than mingling with Meera Syal - author, scriptwriter (Bhaji on the Beach), actress and comic (co-creator of BBC2's much-admired Goodness Gracious Me).
When it comes to classical music, Blair could include the deaf percussionist Evelyn Glennie on his party list. Composer George Benjamin, 38-year-old artistic consultant on Radio 3's Sound in the Century, is about as hip as classical musicians get, and should be included among the Number 10 canape-munchers.
Despite his loud insistence, Chris Evans has never, ever been cool, so Robin Cook is safe in his role as the token ginger at Number 10. Leaving Evans to stew, Blair should call Radio One DJ Mark Radcliffe round to play instead. Admittedly, in a desperate ratings hunt Radcliffe was kicked to the lunchtime slot to make way for Zoe Ball and Kevin Greening's breakfast show, but he has just won a Brat award, and is therefore officially cool.
On the night of the party, as Blair waits excitedly in his tuxedo for the hip brigade to file into Number 10, his guests might like to reflect how much cooler it would be to stand the Prime Minister up.
Better still, they could follow in comedian Harry Enfield's footsteps. Invited to a Prime Ministerial shindig last year, Enfield downed copious amounts of free champers and drunkenly demanded of Blair that he sack Peter Mandelson.
Enfield was later contrite. "It was very rude and not at all clever to be drunk and abusive to the Prime Minister and other members of the Government," he said. Pretty cool, though.