What about a neat, corporate, businesslike "lounge" suit? That's it. A break from stuffy, elitist City tradition, a kind of Chancellor of the Exchequer's "dress down for Friday" outfit, the evening equivalent of Tony Blair's ordinary-bloke-taking-a-weekend-break-at-Chequers look.
But far from appealing to City boys and girls, who love dressing up, the Chancellor may well look a bit of a prig. And possibly a prat. No one is fooled by gestures towards classlessness (there is no such thing in class-driven, class-divided Britain), while those who make a point of refusing to wear a DJ to a Mansion House dinner or a tie to a crusty gentleman's club are little different from those uptight or lazy types who turn up to a fancy-dress party without a costume. Aside from being an insult to hosts and fellow partygoers, it looks all too stand-offish.
If this is so, what is the Chancellor up to? What it looks like is an exhibition of his and the Government's desire to appear matter-of-fact, no-nonsense and nose-to-the-grindstone in their dealings with the City and other institutions. The City is very gradually becoming less formal at the edges, with staff turning up to banks in casual dress - or rather, immaculately pressed casual dress - on Fridays and days when they won't be meeting people. City types are also dealing with a new generation of business clients. These include the multi-millionaire computer nerd, the software tycoon, the advertising crowd, and, if not now, then very soon, the smug young art dealer, the conceptual artist and the video geek. Do these people want to sit down with smug Oxbridge types in loud pinstripes? Perhaps they do, because when City types and Sloanes go casual, they are so extraordinarily well-groomed and have so obviously led a life in which they have never missed a meal, much less a vitamin, that they are more likely to lose the faith of clients for whom, at least, a bespoke chalk- stripe spells banking loud and clear, and, equally, for whom the gleaming casual look is as alien as it is insincere.
The same applies to barristers. We expect them to be snappily dressed. They are not solicitors. They are actors, able to write their own lines as they act. They need to stand out, and perhaps it is safe to say that barristers are, for the most part, naturally flamboyant.
The "lounge" suit is, in some ways, rather sinister. It suggests, unlike the self-confident and stylish dress of barristers and bankers, a kind of corporate anonymity, power without a face, a highly controlled world where there is no room for individuality.
In any case, dressing down is a bit of an insult to people who like to dress up, and that, on big nights out and special occasions, is most of the population. The last Labour politician to dress down self-consciously was Michael Foot. When, as leader of the party, he turned out on Remembrance Day in a donkey jacket, it was widely seen as an insult to both the quick and the dead.
If, however, you know how to dress differently, yet stylishly, you can break the mould on almost any occasion. No one would have expected Mahatma Gandhi to turn up for a drinks party in a DJ. In fact they would have been disappointed if he had. Earlier in his career he did indeed dress up like some pukka young nabob. The dress (or lack of it) he adopted in later years was as much for effect as because he felt comfortable that way. T E Lawrence wowed international conferences by dressing up like an Arabian prince. Che Guevara stole the floor at the UN in New York in 1964 by turning up in green fatigues (he wore these at home, at work and at war).
We like leaders to dress up. We like fancy dress. But we also like to fit in. And this doesn't contradict our love of looking good. If an invitation says DJ, here is an opportunity to brush down the glad rags and look like part of the crowd. Gordon Brown's decision to wear a lounge suit at the Mansion House may seem a trivial affair, but it does point to the heart of the inverse snobbery that will make those of us suspicious of New Labour (puritans? busybodies? holier-than-thou do-gooders?) justified in our suspicions. Why is this Government so obsessed with style, of both dress and address? Is it a case of style over substance? Whenever governments have been over-keen on issues of dress, they have tended to pursue disturbing agendas. Cromwell's Puritans spring to mind (New Model Army, New Zealots), as do Chairman Mao and his cloned cohorts, and politicians representing other unsavoury regimes.
The politicians we can truly believe in (whether we think they are right or wrong is another question) are those who appear true to themselves. This is why people from all sides of the political spectrum like Ken Clarke, outgoing chancellor. What you see is what you get. The same is true of that stylish bounder Alan Clark. Scruffy or dapper in appearance, you could never accuse them of being anodyne, nor of being told what to wear by PR consultants.
It may be true, of course, that many politicians really don't have a clue about clothes (and why should they?). "Blair's Babes", blazened across broadsheet Page Threes last week, were a glorious indictment of the patronising nanny-knows-best school of blue-stocking, middle-class dress. They all look like school governors, members at least of that tribe of fearsomely competent women who run virtually every charity or arts organisation you can think of. But wouldn't at least some of these ladies like to dress up in a glittering long frock for a grand dinner? Presumably not, for surely clothes are unimportant ...
And there's the rub. Clothes aren't unimportant, as "Mandy" Mandelson and Tony Blair know full well. Most humans enjoy clothes and will dress up when they have ready access to beautiful materials or money, or both. Politicians have always dressed up. Julius Caesar wouldn't leave home for the Senate until his body hair had been removed (it was fashionable, and useful, to look like a statue of a god). Hitler sported lederhosen for Bavarian festivals, a simple soldier's uniform for party rallies, but a DJ when soliciting bankers. Stalin dressed like a "proletarian" street fighter until the Great Patriotic War of 1941-5, when, to strike the right image, he dressed like the marshal of an imperial army. Jack and Jackie Kennedy were and remain style icons. Margaret Thatcher dressed up. Churchill dressed up (purple velvet boiler suits, World War One uniforms, ladies' silk underwear, white tie).
Gordon Brown will stand out from the crowd at the Mansion House, but for all the wrong reasons. If the Labour government represents the triumph of workaholic men and women in drab suits, it is time for the rest of us to dress up in style to defy the new and patronising dress-down puritanismn