Stephen Bayley: Tony and Cherie are just like the Beckhams - though not as grand, of course

I did not see Posh 'n' Becks, seasonally repeated on Parkinson (I was clearing out a kitchen cupboard or something else more compelling), but it was impossible even for me to miss Tone 'n' Shree's departures en vacances, an event now treated with great solemnity by the press. Pharaohs were trivialised and the very pyramids shrank in comparison with the Blairs' combined mediagenic stature.

The Beckhams and the Blairs share a modern British obsession with their togetherness. It's a near orgy of handholding and simpering, the Smug Marrieds of Bridget Jones's imagination come to life in two very gruesome pairings. Granted, the nation needs its symbols of uxorious bliss. You might expect to look to the royal family, but there is something woefully anachronistic about the House of Windsor since Diana: a fustian grimness and primness reign. These are regal attributes, certainly, but not ones in tune with the more brassy spirit of the age.

Mrs Beckham and Mrs Blair have a terrifying authority – inside those toothy smiles lurk tungsten-coated, high-density egos of awful aspect. Irony, one suspects, is not a natural ingredient of these women's characters. Comedic dress sense apart, cheerful humour is missing from the public projection of their personas. Each is a mistress of self-invention: Mrs Blair had to outrun a boozy, tactless dad and flaky half-sister, Mrs Beckham had a past in Broxbourne, Herts, to contend with.

As for the men, they are each Goldenballs in their own spheres. They're good-looking in a not-quite-there way and rose to the peak of their respective professions early by the deadly effective practice of special arts: one can dribble, the other does drivel with similar facility. Whatever, they make their colleagues and opponents look flat-footed and dull. Each appears somewhat put-upon – as if they don't get away with much at home. I suspect that when Cherie shouts "Tony!" his first response is to duck.

Cherie in her domestic pomp would, one imagines, be a critically emasculating opponent, just as poor Becks told Michael Parkinson that he lived in fear of Posh's bad moods. Perhaps denied authority at home, the Prime Minister tends to exercise his frustrations on a hapless electorate, unable to hit back for the next four years. Becks, on the other hand, so mutely consummate on the field, remains content to be a beaming Ken when out with Barbie on the town.

And each couple has its problems balancing an insatiable hunger for publicity with sudden attacks of shyness. Never mind that public servants arrange photocalls during their holidays to satisfy what Downing Street deems to be an overwhelming appetite for Blair imagery, nor that Mrs Beckham wanted to be as famous as Persil Automatic, both the Blairs and Beckhams get majestically twitched when the media becomes rapacious. If I wanted a life of modesty and seclusion, I'd think twice about asking OK! to my wedding or having Mary McCartney photograph my fourth-born. But as our surrogate royals, the Blairs and Beckhams transcend rational calculus. It is as if the laws of consistent behaviour were suspended for their benefit.

The imitation of royalty extends to the bizarre dress sense. Mrs Blair's Egyptian trousers were astonishing. She looked as though a provincial amateur dramatics company had been commissioned to perform an entr'acte for the Cirque du Soleil. As for Tony's trainers, if I thought there was a message of solidarity for transit passengers through Terminal Three I'd say, OK, yes, maybe. As it is, I think he looked a gormless twerp. And this was the Blair who, in support of leading British fashion designers, once had his family pose in Tuscany camouflaged in Ralph Lauren. At least with the Beckhams there is a glorious consistency in their following of high fashion.

But even I admit one area where the Blairs and the Beckhams perform with authentic royal style. This is not in the cruel exposure of chat shows, but in the quieter, intimate domestic rites. With unforced zeal, each couple seems fiercely proud and protective of its children. Whether the four Blairs or single Brooklyn, you get a convincing sense of a real family behind the façade. It is the hint of normality among the fakery that is their appeal and, I hope, their salvation.