Television: Safe and Sound (BBC1) Jasper Rees wonders just how many more cheerfully absurd plotlines can be woven into this charming Celtic whimsy

When a woman in part four of Safe and Sound is described as "a bit of a character", she's only come down with the condition everyone else has had since episode one. Another cockle-warming ladleful of Celtic whimsy from the hyperactive drama department of BBC Northern Ireland, the show has more than its place of origin in common with Ballykissangel. Like Kieran Prendiville, author of Ballykissangel, Timothy Prager can lay claim to not a milligram of Irish blood.

As if pinning the place down were not hard enough already, the institution and failure of the ceasefire put its own spanner in the works. Safe and Sound was conceived before the IRA laid down their Semtex, commissioned and filmed after that seismic shift in Provincial history, but only screened once the bombing had resumed. The script, therefore, nimbly hedges its bets. Of the two central characters, lifelong pals across the religious divide who run (down) a garage together, the bumbling Catholic Tommy (Des McAleer) is properly sceptical about the durability of the peace. When he has to care for a querulous dog at the garage he builds a protective "peace line" of spare tyres to keep the mutt at bay. Dougie (Sean McGinley), meanwhile, has far-fetched ambitions in love and in business: he sees in his pathetically unrequited pash for Tommy's sister Eleanor the chance to bridge the sectarian gap.

This is all by way of prominent backcloth. The writing works just as hard to keep the giggleometer active, sometimes too hard. In last night's story an old flame of Tommy's returned from England. Now a nurse, she diagnoses a dodgy ticker for Dougie. "I doubt that," quipped Tommy to his buddy: "You don't have a heart."

Prager's resistance levels to the weak Chaplinesque sight gag are also dangerously low. But much of the humour is more satisfactorily oblique, and powered by a refreshing brand of chirpy sarcasm. When Dougie discovers that a man has been chewing the fat in Eleanor's bedroom, he wants to know what happened: "Do you want me to draw you a picture?" says Tommy.

Tommy's own romantic entanglement is the only one that verges on the realistic. His marriage to tough, practical Maggie blows hot and cold in every episode. Like Dougie's infatuation with the slatternly Eleanor, the brittleness of the relationship is a narrative strength. On-off romances are the very life-blood of long-running serials. You do wonder, though, how many cheerfully absurd plotlines Prager can sew into this basic fabric.

Last night's ended with a web of conversational misunderstandings. Though a theatrical conceit, it was as cleverly filmed, and indeed written, as anything out of Jon Byrne, the high priest of Celtic whimsy, to whom all practitioners of whatever nationality make obeisance.