Two odd, seemingly disconnected thoughts found themselves rattling around in my silly-season skull yesterday. The first was to wonder whether the secretive Gordon Brown, in launching his nuptial coup de théâtre this week, had taken the precaution of first informing the bride. On TV, his former press secretary, Charlie Whelan, made so much of the marriage being conducted Gordon-style, and was so emphatic that the honeymoon might be enjoyed on Cape Cod (because Gordon liked it there), that any viewer might have been forgiven for assuming that Gordon was marrying himself.

Two odd, seemingly disconnected thoughts found themselves rattling around in my silly-season skull yesterday. The first was to wonder whether the secretive Gordon Brown, in launching his nuptial coup de théâtre this week, had taken the precaution of first informing the bride. On TV, his former press secretary, Charlie Whelan, made so much of the marriage being conducted Gordon-style, and was so emphatic that the honeymoon might be enjoyed on Cape Cod (because Gordon liked it there), that any viewer might have been forgiven for assuming that Gordon was marrying himself.

My other bonce-disturber concerned The Independent's Ivan Massow scoop, in which the rich, handsome (and therefore deplorable) gay chairman of the Institute for Contemporary Arts, revealed that he was quitting the Tories and joining the party of Brown, Blair, marriage and the family. "Ah!" I said to myself, "that's the gay millionaire vote tied up for Labour!"

The next phase was - inevitably - the baiting of Massow for his turncoatery. One of the first to condemn him was Derek Laud, the black, gay, Tory master of hounds. Laud took Massow to task for joining a party that, however much kinder it was to gays, was irredeemably anti-hunting. The gay Tory thing might be unfortunate, Laud agreed, but when it came to blood-sports, "behind the Blairite Cheshire cat grin, lurks the true snarling face of Labour intolerance." Tough one, Derek, asking a man to choose between what he irrevocably is on the one hand, and one of his hobbies on the other.

On the left, some were unwelcoming, accusing Mr Massow of naivety. One commentator argued that Massow's decision to defect over the Tory attitude to minorities was somehow contradicted by his (by implication, more important) commitment to the market and free enterprise. The economy, she seemed to be saying, was the weighty base, and all this gay and asylum-seeker stuff was but flimsy superstructure.

Defectors have to get used to this kind of stuff. Many Britons profoundly dislike the idea of disloyalty and infidelity, whether it be to partner of party. Once you're in, you're in. So there is thought to be something slightly oily and unmanly about the party-shifting Shaun Woodwards, the Peter Temple-Morrises and (a longer time ago) the David Owens of this isle.

And it is true that some defections are more credible than others. Take the case of 1995 Labour-to-Tory defector, Leo McKinstry, who suddenly discovered (having weathered the Benn years) that he possessed the brain of Norman Tebbit, trapped inside the body of an Islington Labour councillor. What kind of operation did it take, one wondered, to entirely remove that useless, dangling appendage, his social conscience?

But there, I've fallen into the trap too. What is remarkable and depressing about British politics is not how many people switch parties, but how few. Parties change, people change, circumstances change. Mr Massow was a young entrepreneur, for whom Maggie represented the possibility of economic freedom in the face of unions and an overweaning state. With the accession of William Hague in 1997, it was not in the least naive to believe that the new Tory idea would be to combine economic and personal freedom. Indeed Michael Portillo's fringe speech at the Party conference that year (I was there, I heard him) advocated just that. Hague publicly endorsed it.

Why Hague changed his mind is a matter for another day, but he did. People like Massow found themselves in the party that Norman Tebbit was happy once more to belong to. Some more flexible politicians, such as Steve Norris, can carve out niches for themselves in the face of such adversity, and thrive. But then, Norris is not himself gay; he did not find his naked self being repudiated at every turn by his clothed self. There had simply come a point where the balance tipped for Massow. The bad outweighed the good.

This is not naive behaviour, this is increasingly sensible, and increasingly in tune with how the voters think of themselves politically. But why should Massow be expected to repudiate everything about the party he has left and accept everything about the party he has joined, as though he was having his brains extruded through one ear and entirely replaced through the other? He is certain to find himself on the pro-market wing of Labour, and well out of sympathy with much that gets said at party conferences and branch meetings.

Let's illustrate this point by looking at your politics, or mine. I am currently (I think) a liberal social democrat. I am indebted to a recent essay by Lord Lipsey in which he attempted to make clear a distinction between liberals and social democrats (the individual above all else versus the collective first). And I found myself nodding at the need for collective action on behalf of those people who might otherwise fare badly, but also thinking that - where possible - people act best in conditions of their own determining.

But I am not a libertarian. Whereas I think there is a rational case for unbanning drugs, I am in favour of bad neighbour legislation and of zero tolerance policing. I want full freedom of information, but I also support government legislation to drive child porn off the Net. I agree with many Greens about global warming and over-consumption, but I cannot accept the views of some Greens on GMOs.

Perhaps some of this applies to you too. So why must we be treated as though we either buy the whole political, ideological ticket and ride the whole darn trip, or not get on the bus at all? Why do Labour and Liberal democrat activists - who often have more in common with each other than with others in their own parties - have to pretend to loathe one another? It is an irony of Ken Livingstone's political past that the self-same inclusiveness, which has been such an attractive feature of his mayoralty, was specifically condemned by him when he was in the Labour party.

As politics becomes more of a consumer-led and less of a producer-led business, party ties will loosen, and people will migrate. Now, of course, there are some dangers in this. If we all refuse to become politically engaged simply because no one party could possibly endorse our very specific portfolios, then nothing will get done. Egotism is the enemy of trust, and if we all walk out on our colleagues at the first sign of difficulty, then any meaningful political organisation will be hard to build.

But egotistic politicking happens already. Take the left-wing Labour MP Diane Abbott. Since the election of May 1997, I cannot recall a single interview given by Ms Abbott, any published letter written by Ms Abbott, or any report of a speech made by Ms Abbott, the purpose of which was other than to condemn the Labour government. Ms Abbott enjoys the support of her party in elections, and is spoken for at those times by a leader she plainly abhors and on the basis of a manifesto she clearly loathes. In her case, it would obviously be more honest to defect, if only there were something to defect to. Maybe she could start something up.

David.Aaronovitch@btinternet.com