RADIO / Dramatic rents in the fabric of history: Robert Hanks on The Lyme Regis Food and Fertility Festival, Singer and the first episode of Hancock's Half-Hour

'If we had all night and another day, and if we had a hundred voices painting pictures in your minds, we'd make you do the hard work for us . . . and if we used a thousand sound effects to con you into thinking you were really there, we still couldn't do what you can do.'

The prologue to Michael Fox's production of Singer (Radio 4, Saturday and Sunday) was apologetic in tone - we're sorry we can't give this play the air of lavish authenticity we'd like it to have - but under cover of that humility smuggled in a large consignment of vanity: the old boast that, because radio acts directly upon the imagination, it is more vivid than any other medium.

John Fletcher's comedy The Lyme Regis Food and Fertility Festival (Radio 3, Sunday) was a victim of the same canard. 'Only radio can do this,' the publicity material trumpeted or, more accurately, tootled under a precis of the plot. In the case of the Fletcher play - of any Fletcher play - you can see the point of that statement. It is set in an era of artistic totalitarianism, when London is patrolled by the Sarah Dunant thought police, and covered with statues to the Blessed Melvyn. Fred and Deirdre escape this sterile prison for the Festival at the prompting of the Pink Fairy, a priapic Geordie in a tutu, hoping to save their marriage. At Lyme Regis, they swim out to the Golden Worm, a maelstrom off the coast which sucks them down and transports them into mid-air above the Cerne Abbas giant. In the course of their subsequent adventures they are dismembered, devoured by crows and excreted back to earth; they travel back through geological time in the Dorset substrata, to be petrified as Purbeck marble in the Jurassic era; are hewn from the rock to become gargoyles in a church; are reconciled and returned to human shape; and shake Death (Bill Wallis) by the hand. Finally, the Cerne Abbas giant and Fred are joined to make a new man, who descends on London to destroy this cultural Babylon and build the New Jerusalem.

All this - lovingly detailed by Shaun McLoughlin's production - would have been easier to take if you had felt that Fletcher was being economical with his ideas, that he had kept some ammunition in reserve; but the impression was of a full-frontal assault, with all weapons discharged. (That's an image disconcertingly appropriate to Fletcher's phallocentric obsessions: one peculiarity of radio is the writer's licence to enjoy full-frontal nudity, too, and here we got an earful of 'enormous whangers'.) But you recoiled from his polemic as from some drunken acquaintance's unsolicited catalogue of sexual paranoia. The ranting against the 'over-educated tossers' of the artistic establishment, 'the vacuous acting of Antony Sher', felt out of proportion - confirming the self-importance of the artist, rather than deflating it. Fletcher apparently feels that radio grants the imagination unlimited liberty; and this assumption of freedom spoiled the play's focus. There was a pattern there, of death and sex and rebirth, but not a dramatic structure.

Singer had other problems. Peter Flannery's play was translated from the stage complete with Antony Sher's mesmerising performance of the title role, an East European Jew who survives Auschwitz to become a slum landlord in the west London of the Fifties - a figure quite precisely modelled on Peter Rachman. But theatrical action transfers awkwardly to radio; in the intimate attention it pays to the individual voice, and the narrative sweep it can present, radio is closer to film.

Sher's acting - not at all vacuous - was skilfully scaled down for the microphone, and he had excellent support from Mick Ford, Malcolm Storry and Jack Klaff; but the production hovered uneasily between the conventions of different media - as in the stylised mannerisms of the English upper classes who alternately patronise and dote on Singer.

The play itself adds a memorable postscript to reality: this Rachman lived on to renounce evil and become a secular saint. But the most vital scenes were those rooted in history: the rent scams and mobsterism, the social pretensions gruesomely exposed at a comic dinner party which bore a curious resemblance to one held by the Lad Himself in the first episode of Hancock's Half-Hour (first heard in November 1952, and repeated on Radio 2 last Saturday) - an episode that is as funny as the later, classic stuff.

Galton and Simpson, like Flannery, portrayed the dinner party as a snare for counter-jumpers, with henchmen masquerading incompetently as servants and consumption vulgarly conspicuous: 'What, run out of cavvy-ary? 'Iggins, gut another sturgeon.' There's even an eerie prefiguring of Singer / Rachman in the character of Smooth- Talking Sidney James, the dodgy letting agent. It seems a shame that Flannery's art should work so hard to mirror life, and then turn out to be mirroring art after all.