But this is only true until one has a go at trying to propagate ideas in any authoritative way, for it's then that one realises that what we see, read and hear is continually monitored and shaped according to some powerful and inflexible economic imperatives. Take advertising: it won't escape the notice of any inhabitant of a large city that the thoughts which greet us in public places are overwhelmingly interested in directing our attention to the advantages of consuming deodorants, airline flights and blockbuster films. If we really lived in a free market of ideas, we should expect that we would occasionally hear a public defence of kindness or a paean to the wise aphorisms of Marcus Aurelius, but we don't, for the obvious reason that few gentle Buddhists or stalwart Stoics have the £100,000 necessary to start an effective ad campaign. Try to interest a TV commissioning editor in a film about deforestation in Sudan and you will politely be told that a little more grit, sex and glamour might be an idea. The same logic plays itself out in radio stations and publishing houses. Our world gives us unparalleled freedom to express ourselves - and yet also an unparalleled freedom to be ignored unless our message is precisely tailored to fit some punishingly narrow categories.

It was from an awareness of the danger of such a situation that the notion of artistic and intellectual subsidy was first formed in the 1920s. As the defenders of regulation put it, the economic free market simply could not be relied upon to generate a diverse and appropriate market in ideas and art. Unfettered, the culture rewarded by the economic free market would relentlessly pull us towards our baser appetites. A further claim was made that this phenomenon would be risky for the whole of society. It would vulgarise us, enhance our crooked impulses, corrupt our children and change our behaviour. A crass culture would make us into crass people.

However, in the later part of the 20th century, such warnings came to seem both hysterical and untrue. Just as one could relax exchange controls and still survive (indeed thrive), so one might relax a range of cultural controls. Governments therefore set about systematically dismantling much of the public-service requirements of the Reithian regime at the BBC. ITV channels were set free of their regulatory demands. It was argued that Channel 4 could forgo public money and fund itself by reality shows instead. Meanwhile in publishing, rules on who could sell a book and at what price were thrown aside to allow the market to rule without restriction. The results of such manoeuvres are now everywhere apparent. We need only cast an eye on tonight's television schedules and the top sellers promulgated by that most powerful force in British bookselling, Tesco's supermarket.