Yesterday was, of course, Election Day. The Labour Party was hoping to double its majority to a comfortable 50, and to consolidate its programme of radical social(ist) reforms under its esteemed leader, Neil Kinnock. In the afternoon, Roy Hattersley and John Biffen discussed the first five years of Labour rule in "What If ... ? (R4): as you'll have guessed, the rest of the sentence goes " ... Labour had won in 1992".

The idea behind this series is to take the seductive notion that things might have been different and tease out what would have happened if they had. There is an odd conceit involved, by which contributors pretend that things actually were different, which is disconcerting to come upon accidentally - to hear Hattersley, who pompously described himself as one of the Significant Three, remembering the victory party which he relished, along with the other triumvirs, Kinnock and John Smith, before taking up his role as a benevolent, flawless Home Secretary.

Or at least I think that's what he was saying. His manner of delivery is so indistinct that, in his long, windy sentences, few words have endings, and the listener is given an extra hypothetical problem: what if he didn't say that at all? Anyway, I'm sure he said that Harriet Harman's little problem over the education of her children never arose. For one thing, there are no more selective schools and, for another, she has not risen to prominence: promoted beyond her ability is how Hattersley sees her now.

The trouble with this kind of thing is that so many other imponderables rear up. What if John Smith hadn't died, for instance - but to ask that is to break the arbitrary rules of this ultimately futile game. The previous edition changed the sex of Queen Victoria, which, in the opinion of the historians involved, meant that the wars of this century would probably have happened in the last.

And Hitler might have lived and died a humble painter and decorator, and Israel would still be Palestine and Jews would have been living peaceably throughout Europe. Perhaps. A clutch of historians were gathered for a particularly stimulating and focused Start the Week (R4) on Monday, discussing theories of history. The most interesting (because he was after the actual truth, rather than whimsical fantasy) was Bill Rubinstein. His book, The Myth of Rescue, counteracts the relatively recent theory that the Allies could have saved more Jews from the Holocaust. He made an important distinction between refugees, of whom thousands were saved before the war began, and prisoners of the enlarged Third Reich, who were virtually impossible to rescue while Hitler lived.

This led to a conversation with Robert Harris, whose novel Fatherland (R4) was broadcast as a play that evening. It was the disgraceful "historian" David Irving who started Harris on his own "What if ... " quest. Irving's contention, that the Holocaust never happened, was partly based on the fact that Hitler's name is missing from all orders to exterminate Jews. Harris thinks this is because Hitler was already planning for a time when he would be able - as Stalin was later - to deny all involvement with genocide.

So the play itself, dramatised and directed by John Dryden, imagined that Hitler had indeed won the war. In 1964 in Berlin, a body is fished out of the river. The resultant investigation, set against a lurid background of the Fuhrer's spectacular 75th birthday celebrations, was a scary whodunit. King Edward and Queen Wallis were planning a state visit, President Kennedy (Joseph, that is) was plainly more corrupt than any of his kin, and the Jews had simply disappeared, "gone east". It was clever and intricate, made a little confusing by the way that most of the men spoke in similar, tense whispers, often against a background of heavy rain.

But it made you very glad that it didn't happen. The whole problem of history on radio is unresolved. Late on Saturday nights Paul Boateng presents his series Looking Forward to the Past (R4), in which various celebs are invited to show off their knowledge by being asked fatuous questions like would you rather be Joan of Arc or Boadicea. It is ponderous and inane and is beginning to sound very tired, especially when guests are increasingly arch about what they would like to put in a time capsule to represent our civilisation to future generations. Benny Green chose a cheeseburger - yuck - and Roy Porter a Wonderbra. Need I say more?

A much better history programme is On This Day (R4) which, every morning, presents the news of 50 years ago, with the help of some of those who made it. Tuesday's edition starred Sylvia Peters who, at 22, became a television announcer and now, half a century on, sounds about 25. It is invariably both informative and comic and is impeccably presented by Geoffrey Wheeler.

As you might expect, R2 has a more overtly frivolous attitude to historical refinement. Ken Bruce's What If Show is really just a succession of sketches and double entendres but it is irresistibly good-humoured and blessed with the talents of Sally Grace, the best impressionist in the business. On Thursday she was a brazen, boisterous Fergie, then a primly flirtatious Miss Moneypenny, then an ancient cave-woman - whose son's winter-solstice present was a remote-control horse and cart, batteries not invented. It's very silly, but at least it doesn't try to be anything else.

Gardeners' Question Time (R4) slipped into history on Sunday when it celebrated 50 years on air. It has always attracted experts with great names - who could forget Fred Loads and Bill Sowerbutts? - and its current panellists include Pippa Greenwood and Bob Flowerdew. Since the well-publicised uprooting of a previous team to Classic Gardening Forum, these seedlings have made vigorous growth and are now established in their new sunny position, climbing towards the top of the tree (sorry, I'll stop this).

In fact, the programme is much better. In the old days, every questioner was subjected to a gruelling and patronising interrogation as to their competence to wield a hoe - have you watered/fed/pruned/sprayed/ mulched/murdered this plant? Whatever they answered was wrong. Ah, the experts would sigh, maddeningly, there's your answer. They are much less earnest now. In the jubilee programme, they were asked about favourite trees. Pippa Greenwood said that she so loved beech trees that she could happily lie on her back underneath one for the rest of her life. Funny, that's how I like to do my gardening, too.