RADIO / A nation that's gone to pot: Robert Hanks listens to the cases for and against the legalisation of cannabis

THE IDEA of worlds that might have been has always been attractive to writers of fiction. In Kingsley Amis's The Alteration, we had a 20th century in which the Reformation had never happened. Philip K Dick's philosophical fantasy The Man in the High Castle, Len Deighton's thriller SS-GB and Craig Raine's tragedy '1953' all took place in the aftermath of an Axis victory in the Second World War.

What If . . . ? (Radio 4, Tuesday), 'the programme that rewrites history', generally proposes slightly more modest counterfactual kinks - a world in which Enoch Powell never resigned from the Conservative Cabinet, say - but for all that the programme maintains an approximate grasp of reality, it is often more disturbing than fiction. That isn't only because the worlds imagined by Christopher Andrew are recognisable distortions of the one we know; it's also because the abandon with which historians pounce on the chance to make it up as they go along suggests a worrying preference for hypothesis over facts. And, finally, it's because the programme rarely seems to tell you anything you really want to know.

Last week's programme took a particularly spicy question: 'What if cannabis had been legalised 25 years ago?' The programme started promisingly with a line from Edgar Lustgarten, speaking in 1967, who said that 'mari-hoo-ana' (a word pronounced with the polysyllabic delicacy you expect from somebody keen to show that they haven't been drinking) 'leads with progressive inevitability to the drugs that destroy the human being'. He went on to talk about those who drop out from the 'rat race of success' and enter, instead, 'the rat-hole of darkness and despair'. Goodness.

Lustgarten seemed to herald an enjoyable Reefer Madness vs Hippy Utopia tussle: but, sadly, the standard of anti-drug rhetoric has collapsed dramatically in the last quarter-century. Pressed for suggestions about the problems that legalisation might have brought, Griffith Edward, Professor of Addictive Behaviour at the National Addiction Centre, seemed to feel that the main hazard was the advertising. Cannabis manufacturers, Edward warned, would sponsor everything from opera to snooker (reader to insert own Pot Black joke). He didn't explain what's wrong with that, though. Surely it's sponsorship by manufacturers of harmful products that you need to avoid, and Edward didn't make much of a case for the dangers of marijuana (though he touched on the problems of schoolboy toking behind the bicycle-sheds, and the risk that cannabis use could lead on to tobacco use - a nice twist to an old argument).

But if he didn't make much of the hazards of cannabis, Anthony Henman, of the International Anti-Prohibition League, wasn't convincing about its safety - when it was put to him that 'seriously stoned' drivers might be unsafe, he claimed optimistically that seriously stoned people wouldn't want to drive. Neither he nor Edward exercised any profound imagination about what cannabis could do to (or for) society. But what the programme really lacked was a moral perspective, some idea of the principles involved.

You got that on The Standard Setters (Radio 4, Sunday), an unusual chat-show hosted by the Rev Dr Edward Norman. Dr Norman's brief is to quiz people 'whose work influences moral attitudes' (according to the Radio Times billing), to find out the basis for their decisions. For the first programme, his guest was His Honour James Pickles. Dr Norman quoted a QC who had said, on Judge Pickles's retirement, that he mirrored the views of the man in the street. The way Dr Norman related it, it didn't sound as though that was meant as a compliment; and populism isn't a charge you could reasonably try to pin on Dr Norman himself, a high Anglican with a refined intellectual bent.

In fact, the two of them got on rather well, thanks to a shared liberalism. Mr Pickles, in particular, waxed perfectly reasonable in his support for the legalisation of drugs and prostitution: you couldn't see why he had such a reputation for querulousness and eccentricity. His view was that an adult should be allowed to do anything to himself so long as he does not harm other people. Street prostitution (as opposed to brothels) should remain illegal because of the harm it does to ordinary people living round about - kerb-crawling, used condoms lying on pavements, and so forth.

The liberal argument seems sensible enough; except that Mr Pickles's definition of 'harm' seems to relate it to mere nuisance value - so making out a strong case for banning, say, alcohol, which leads to loud, irritating behaviour, piles of vomit lying on pavements, and so forth.

The facade of reasonableness broke down, though, when Mr Pickles confessed that he would find it difficult to vote for a homosexual: 'One ought not, of course, to be prejudiced against a homosexual because of his sexual predilection. On the other hand, we do know that such people tend to have what you might call twisted characters . . . ' There aren't many interviewers who can get such damning admissions so easily: you would do well to follow Dr Norman's career with interest.