In the days when there was a Radio 4 programme called Stop The Week, with Robert Robinson, people who didn't like the programme used to tell me the trouble with it was that as a discussion programme it never got anywhere. I agreed with this, but I alwaysfelt they were judging the programme on entirely the wrong basis.

"Ah, but Stop the Week is not a chat show at all," I would say. "It's a soap opera! It's a mini-Archers!" All those people - Bob Robinson, Ann Leslie, Laurie Taylor, Milton Shulman - form a little family and have developed their own slightly fictional characters within it. They have their spats, they have their foibles, they have family jokes (about Volvo drivers, for instance), and when things are getting a bit heated, maybe because precocious cousin Laurie has been annoyed by something that waspish Bob has said, then Uncle Milt Shulman "steps in" with one of his wise Jewish stories about Goldstein, and everyone calms down waiting for the punchline, or perhaps they all turn on Uncle Milt and say: "Not another of your damned stories ...!" It's a soap. People switch on to hear the characters, not the talk.

I had forgotten about this winning theory until I found myself listening to The Moral Maze the other day and realised suddenly that exactly the same is happening to that programme, and that the reason why people express such differing opinions about it is that they don't realise that it is becoming a soap opera.

Ostensibly The Moral Maze is a discussion chaired by Michael Buerk in which Edward Pearce, David Starkey, Janet Daley and Rabbi Hugo Gryn leap upon a modern Gordian knot and leave it more convoluted than they found it. But really it is a soap opera in which Pearce and Starkey have a go at each other, Janet Daley has a savage go at the witnesses, Michael Buerk has a gentle go at restraining them all and, just like Uncle Milt Shulman, the rabbi - probably Lionel Blue's elder brother - tells a story if there seems no other way of ending the programme. It's the melodrama of character that sells the programme, not the solving of modern problems.

I know this, because yesterday I was listening to the programme when they were discussing male and female gender roles, and, instead of agreeing or disagreeing as I went along, I was actually thinking: "Never mind the agenda, where's David Starkey? Why aren't David and Edward having a go at each other?"

And they do have a go at each other. In one recent discussion on homosexuality, David Starkey, who had freely admitted to being gay, was addressed mockingly by Edward as "David, dear".

Some other time, Starkey (the new Gilbert Harding?) was defending capital punishment, and Pearce mocked him for wanting cheap thrills. "I get all the cheap thrills I need from you, Edward," said Starkey.

Not yesterday. Yesterday, instead of Starkey, they brought in Roger Scruton, the man who not only brings intellectual rigour to a chat show, but has everyone looking at their watches within five minutes of the start, and not once did he and Edward come to blows, I think. What a waste of an episode.

The fact is that you can't really stop this sort of chat show developing into a soap, if it has enough regular characters, and you can't make it happen if there isn't a regular repertory.

It tended to happen to Loose Ends (especially when Robert Elms and Brian Sewell went off on engaging picnic trips together) and it happens a bit in I'm Sorry, I Haven't a Clue, where Humph pretends to despise the resident pianist and has even invented several fictitious characters. But you can't make it happen on Any Questions? and Start The Week and Question Time, because there is a completely new panel every time.

On such programmes as Start The Week and Any Questions? the only constant factor is the chairman. Now, there are one or two ways in which the chairman can compensate for his lack of a repertory company. He can bring in sidekicks, as the Americans tend todo, and as Melvyn Bragg does with those female journalists he imports one at a time from the Independent and Times. He can work up one of those depressingly jocular opening monologues in the manner of Clive James or Clive Anderson or Ned Sherrin even. Jonathan Dimbleby attempts it with his joky introduction of panel members on Any Questions?

But it's hard work for one man by himself. Far better to switch on The Moral Maze every week to enjoy their wrangles, to listen to the witnesses (many of whom seem to believe that they have actually been asked there to give their opinion instead of, in reality, to act as chopping blocks for the regular characters), and to wonder when Edward and David will actually come to blows.