How would we tell if the BBC were biased? The wrong way of doing so is the way used by the corporation's own executives and representatives. The BBC's staff are so enclosed in a world of left-liberal assumptions that they do not even understand the question. They think they are being accused of explicit support for the Labour Party, openly expressed in their output. They fend off accusations of partiality by saying (rather questionably, but that's another argument) that they are strictly neutral between Labour and the Tories. They once sought to prove this by removing Melvyn Bragg from the chair of Start the Week when they discovered (seemingly to their amazement) that he might be a Labour Party supporter. This possibility became apparent to them for the first time when he was made a Labour peer. Yet Bragg's elevation somehow did not stand in the way of his swiftly becoming the presenter of In Our Time. The BBC's dim inability to see how funny this is, or how far from the point, would itself be funny if its results were not so damaging.

I recall a few years ago a group of BBC staffers making what they thought was a killingly amusing satire - which they proudly showed at the Edinburgh TV Festival - on the idea of an impartial news bulletin, as allegedly imagined by conservatives. Since they had no real idea what a conservative is or thinks, the film was clueless, full of blatant right-wing editorialising and sycophancy towards an unnamed corporate boss.

Were I a multibillionaire, I could commission the proper research into nuance, tone of voice, who gets the last word, presenters' backgrounds, running order, drama, soap operas and cultural coverage, that would demonstrate beyond any doubt that the BBC is on the side of the cultural and social revolution that I and many other licence-fee payers oppose with all our hearts.

But I am not, so I shall rely instead on personal experience. I could, if there were space and I were nasty enough, list here many instances of the BBC's near-horror of the conservative person; its nervous need to allow them on, but its extreme difficulties in treating them fairly when it does; its refusal to let them anywhere near presenters' chairs (the seats of power) unless the audience is tiny. I would detail instances of its failure to understand what conservatives think, or to pay any attention to what they say - the current affairs producer who thought Melanie Phillips and I agreed about the Iraq war, and the researchers who called me up in the hope that I would make the case for torture, or for arbitrary imprisonment, spring to mind.

I could dwell on the assumptions of programmes such as The News Quiz and Have I Got News for You, which depend for their humour on the belief that everyone in the audience thinks (I encapsulate here) that socialism is basically good, that religion is bad for you and the monarchy is absurd. "Do you really think," a senior radio executive, apparently intelligent, once asked me with a puzzled frown, "that The News Quiz is a left-wing programme?" This was one step down from the presenters of current affairs programmes who would demand of me, when I was allowed on in an honourable but nervous attempt at "balance", questions that always began "Are you seriously saying . . . ?".

They could not believe that I, an educated human being of their generation, held the opinions I hold. They had never, in the course of their long and comfortable journey from their Oxbridge junior common rooms to White City or Portland Place, ever met anyone who did not share their assumptions, whom they hadn't also felt able to despise. Even worse, perhaps, was the knowledge that I was once on the left myself, though they are keener to acknowledge my Trotskyist period (obvious extremist, you see) than my long stint in the Hampstead Labour Party. That is not to say that they do not despise me, too, but I make it difficult for them by not being Nick Griffin, Alf Garnett or Geoffrey Dickens. Sometimes I make it so difficult for them that they stop asking me on at all - not because they disagree with me, but because they agree with me. During the Iraq war (with the significant exception noted above), my invitations to take part in radio and TV discussions shrivelled to nothing. Opponents of the war were good. "Right-wing" people were bad. I was "right-wing" and against the war. It did not compute, so I was dropped.

What troubles the BBC is not a party bias. On the contrary, the BBC is so powerful that it has now succeeded in converting the Conservative Party to its point of view, and rewards it with increasingly extensive and sympathetic coverage. It is a set of potent cultural, moral, social, sexual and religious assumptions, which touch on all topics from cannabis to the EU, and which affect everything from the plot-lines of The Archers to the use of the metric system on nature programmes. I cannot say how sad this is for the dwindling numbers of British conservative people who value the BBC as a national institution and do not wish to see it swept away. I wish it were not so.

Peter Hitchens writes for the Mail on Sunday