RADIO / Gospel according to Tap: Robert Hanks listens to a history of heavy metal and a reconstruction of the Chicago Conspiracy Trial

SUMMING up the Chicago Conspiracy Trial in last night's reconstruction on Radio 4, one of the participants said: 'We saw, perhaps, the evil of banality, the danger of mindlessness, and the danger of banality fused to muscle.'

Which, at times, is rather the way you felt listening to For Those About To Rock (Radio 1, Saturday). In the second and final part of Wendy Pilmer's sharp history of heavy metal, Bruce Dickinson took up the tale in the late Seventies, when punk forced metal underground and the loud pomp of Deep Purple and Black Sabbath was replaced by new moods - more aggressive, more basic, more extreme and, to be fair to most of those involved, funnier.

Metal is riddled with genres and sub-genres - the list includes hate metal, thrash metal, punk metal, speed metal, death metal, doom metal and black metal, although one rock journalist admitted he didn't know what the difference was. But the really big division revealed here is between the metal bands who like to claim that the Spinal Tap film was based on them personally, and the ones who think it was a deeply unfunny and wildly inaccurate parody. To emphasise the importance of the group in HM's self-image the title of this episode was 'an incredibly Tap-ist thing'.

This awareness of its own absurdity is metal's saving grace. The genre encourages a particular sense of humour: ironic and self-deprecating. It's not unlike Jewish humour, arguably because it's bred by conditions that are related in kind, if not in scale: metal fans feel themselves oppressed and shunned by society at large (the phrase 'ghetto mentality' cropped up more than once).

One effect of this is an ambivalence towards the machismo usually associated with the genre - the guitar as extension of what one speaker called the 'oojah-ma-flip'. Most of the metal performers interviewed seemed to find acting butch embarrassing; many felt that it had to be tongue-in-cheek to be entertaining. But tongue-in-cheek machismo isn't easy to tell from the real thing, and many of the interviewees still kept a naive faith in a narrow version of masculinity. You couldn't replace the members of Kiss with females, one man pointed out, leaving moot the question of whether you could replace them with humans at all.

The division between the ironists and the rest was also apparent in The Chicago Conspiracy Trial, in which an assortment of yippies and peace protesters was charged with conspiring to incite the riots at the 1968 Democratic Convention. This version, produced by Martin Jenkins and John Theocharis, used the memories of participants and transcriptions of the five-month trial. Its strength lay in its length - more than two hours without a dull moment - and excellent acting.

The trial was largely a contest of styles between two Hoffmans, the humourless, conservative Judge Julius J Hoffman and Abbey Hoffman, leader of the defendants, who spent his time doing amusing things like blowing kisses at the jury, sprinkling marijuana on the flag, and wearing judge's robes into court, then taking them off and trampling on them.

Bobby Seale, chairman of the Black Panthers, didn't join in his co-defendants' games; instead, he continually interrupted to insist on his right to conduct his own defence and to accuse the court of racism, disrupting proceedings to the point where the exasperated Judge Hoffman packed him off to serve four years in jail for contempt.

As somebody pointed out, Seale thought of himself as different from the others - he was a real radical, they were just 'candy-asses'. Hoffman was prejudiced and draconian, but he at least did Seale the courtesy of taking him seriously; and there's a more interesting kind of irony in that.