Not that Del Boy would have even been troubled by the absence of quality control, but Only Fools and Horses continued several series past its sell-by date and ended up a pale, and stale, imitation of its once great self. Writer John Sullivan then flogged the dead horse even further by giving the least interesting supporting character, Boycie, an ill-judged and mirth free spin-off, The Green Green Grass.

So my expectations were suitably low as I approached Rock & Chips, a feature length Only Fools and Horses prequel set in 1960.

Guess what? It was terrific. Freed from the tyrannical demands of a studio audience, Sullivan was able to explore his characters in greater depth, fashioning a genuinely moving love story infused with poignancy and charm. The laughs may not have come as thick and fast as in Only Fools' sitcom heyday, but the comic moments were of the highest quality and beautifully crafted into the narrative. For once the description comedy-drama was fully appropriate.

Sixteen year old Del Boy (James Buckley) and his Nags Head cronies were all present and correct, seen mounting the first rung on the entrepreneurial ladder by selling nylon fibre carpets that electrocuted anyone who set foot on them. However, the focus of the film fell upon Del's mother Joan (Kellie Bright), and how she met Rodney's father, career criminal Freddie "The Frog" Robdal. In a crowd-pleasing piece of casting, Nicholas Lyndhurst played Robdal and did a fine job of it, nicely capturing the conflicted emotions of a ruthless, self-serving, amoral ex-con bewildered by love.

The period setting was lovingly recreated, the performances top notch and the script - apart from a couple of instances where Sullivan needlessly spelt out the jokes - was first class. Lovely jubbly work, John. Now leave it alone.

Rock & Chips - which one could either regard as the prequel to Only Fools and Horses or the prequel to The Green Green Grass, depending on how gloomy one wanted to feel about the state of commissioning in British television.

As a 90-minute pilot, the conceit was, presumably, to show us what one of Britain's best-loved TV characters - Del Boy - was like as a teenager; hanging out with a similarly acned Trigger, Denzil and Boycie. Kind of like they did with Muppet Babies, but with Cockneys. You Muppet Babies, perhaps.

The point of the pilot was that Joanie - Del's brassy, put-upon mother - had to have an affair in which she conceived Rodney, so that Del Boy has someone to shout "You plonker!" at if Rock & Chips goes to series.

To this end, Nicholas Lyndhurst turned up as Freddie "The Frog" Robdal, in order to impregnate Joanie with the character he will later play in Only Fools and Horses. Technically, it's quite hard to categorise what such an act comes under: self-incesting? It's kind of like a paradoxical, existential uroboros. Or, in a nutshell, "Eugh - kinky TARDIS Rodders-sex".

Intriguing time-travel ethics to one side, however, Rock & Chips was, at root, a feature-length dose of nothing: the period details of the Formica-topped tables holding more interest than wringing out, and re-using, these tired old characters from Peckham yet again. Please, BBC, let them die. I've got to square with you: they really weren't that interesting to begin with. They should all have just been background extras in Minder.

Rock & Chips was a strange affair, a 90-minute amplification of one of the running gags in Only Fools and Horses, that concerning Rodney's dubious parentage. All the old gang - Del and Trigger and Boycie - were on hand as schoolboys, but John Sullivan's drama was less interested in them than in the brief affair between Joanie, Del's mum, and Freddie "The Frog" Robdal, a career criminal, played here (naturally) by Nicholas Lyndhurst. Less interested, too, in straightforward sitcom than an unsatisfactory hybrid of classic Trotter cheekiness and something much more melancholy and heartfelt. The soundtrack was like an antique jukebox and there were some sly touches of period detail (a cigarette machine in a hospital waiting room), but the narrative's focus was blurred and the pacing weirdly off - quite a lot of the time you were well ahead of the drama and hanging around for it to catch up with you.

In its one-off revival last night as Rock & Chips, Only Fools and Horses, the BBC's over-loved hit from the Eighties and Nineties, performed a genre-bend. A broad, sentimental, Cockney sitcom became a comedy-drama of charm and subtlety that did its writer John Sullivan nothing but credit. It is possible, I concede, that as an irregular viewer I missed nuances in the original, but for most part Only Fools stays in the mind - does it not? - for the chandelier smash, Rodney and Del Boy's foggy transformation into Batman and Robin, and David Jason's perfect fall through a non-existent bar, a moment pilloried with splendid unfairness by the comedian Stewart Lee for being repeatedly voted television's funniest moment.

There was almost no physical comedy in Rock & Chips, a prequel set in 1960 (it felt earlier). Del Boy was a teenager, Rodney not yet born and their mother, Joan, not merely still alive but, in Kellie Bright's winsome portrayal, still sexy. (I'll never think of Kate Aldridge, whom she plays in The Archers, in the same way again.) The 90 minutes' broadest point was Phil Daniels's moustache, donned to complete his misjudged turn as Grandad. Joan's boss's lascivious attentions to her bosom would also count as seaside postcard humour were they not undercut by the seediness of his masturbating after each of their encounters.

Instead of big laughs we were delivered a genetic explanation for why Rodney was as he was in Only Fools: melancholy, disappointed, brighter intellectually than his half-brother Del but without his neon-glare personality. His father, an unknown quantity in the series, turned out to be a ruthless jailbird with an artistic streak called Freddie Robdal (pun), who seduced his mother right under the careless supervision of Del's idle father, Reg. Nicholas Lyndhurst who, of course, played Rodney, here played his father, Freddie, and produced a detailed performance that suggested the con's psychotic tendencies could be tamed by the right woman. It was from Freddie that Rodney must have got his brains, for Joan was so thick she did not get a single joke that Freddie pushed her way. From Joan, he clearly inherited his stoical sadness.

As the really boyish Del Boy, James Buckley conveyed during his relatively brief screen time his Oedipal feelings for his mother and an early surefootedness in business, if not in society. Joan, looking down at her new baby, predicts, not unreasonably, that Del will be rich one day. From another high rise Freddie looks down on them. She nods her head. He raises his glass in pride. His paternity has finally been acknowledged. The question posed by Rodney in the last Only Fools and Horses, did his father love his mother, has been answered. Full of astute period details, such as the family planning clinic where a room of Mrs Smiths await their pregnancy tests, and with enough good lines to get by on (a snail looks like "a bogey in a crash helmet"), Rock & Chips was better than the sequel that preceded it.

There are many for whom the words Only Fools And Horses spell comedy gold. The Peckham-based misadventures of Del Boy and co habitually figure in all-time greatest sitcom lists and there can't be anyone left alive who hasn't seen David Jason fall through the bar at the Nag's Head. Like it or not, Only Fools And Horses has become part of British folklore. So as someone who never really got the whole lovely-jubbly lark, it was hard not to approach Rock & Chips without a touch of trepidation. This prequel from writer John Sullivan threatened to be 90 minutes of in-jokes about characters I never cared about in the first place, stuffed with references that would fly straight over my head. But knock me down with a filched feather duster, if it didn't turn out toan understated slice of bittersweet nostalgia.

The first mildly weird thing Rock & Chips had going for it was that Nicholas Lyndhurst was playing the dodgy criminal who turned out to be Rodney's dad. Given that Lyndhurst will forever be linked at the hip to the gormless Rodders, it felt oddly incestuous watching him seduce Mrs Trotter in a liaison that would climax with him fathering himself. Or maybe that was just me. There were more major plus points in the performances of James Buckley (of The Inbetweeners fame) as the young Del Boy and Kellie Bright as his sainted mother. Transcending the clunking staginess and looming sentimentality that threatened to scupper Rock & Chips at any minute, Buckley and Bright seemed beamed in from a classic black-and-white kitchen sink movie of the 1960s. They deserved a show all to themselves.

Though it was strangely unconvincing in its period detail - everything looked squeaky clean and lifted from the BBC props cupboard - and had more than the odd lapse into knucklehead farce, Rock & Chips was more than a mere vanity project for John Sullivan. Somehow it made me care about the Trotters in a way decades of Only Fools And Horses never came close to.

We've known for a while that there wouldn't be any more Only Fools And Horses. But creator John Sullivan is happy to wind back the clock instead, taking us back 50 years for this feature-length comedy-drama, focusing on the Trotter family's early years.

Set in the less-than-swinging Peckham of 1960, the story centres on glamorous (in a low-budget kind of way) cinema usherette Joan Trotter, played by Kellie Bright, along with waste-of-space husband Reg (Shaun Dingwall) and their teenage lad Derek - hanging out with pals Boycie, Trigger, Denzil and Jumbo Mills and already showing entrepreneurial tendencies.

Only Fools' Nicholas Lyndhurst is "art connoisseur" Freddie Robdal, fresh out of jail and set to cause ructions in the Trotter household.

You won't get any clues from the terrible title, but this feature-length chunk of rosy 1960s nostalgia is a "prequel" to the beloved Only Fools and Horses, which left our screens for good in 2003. Doubtless there'll be a ready-made audience of millions for John Sullivan's fond look at the beginnings of Del and Rodney Trotter, and their hopelessly small-time business empire. As for anyone else, it will depend on your tolerance of cheery cockney wide boys and diamond geezers. There's no David Jason - Rock & Chips' Del Boy is a cheeky, mouthy fresh-faced teenager who's already a bit of a wheeler-dealer - as this is really the story of Del and Rodney's sainted mum, Joan (Kellie Bright), a beehived, brassy, hard-working woman who's married to a layabout. But Joan's head is turned with the return to Peckham of the suave crook Freddie Robdal after ten years in Dartmoor. He's played by Nicholas Lyndhurst and Only Fools devotees will be in on the joke straightaway, as they all know that Freddie "the Frog" was Rodders' dad. Don't expect broad Only Fools belly-laughs, though; just gentle smiles of recognition.

John Sullivan's one-off drama sees the return to TV of his most famous creations, the Trotters of Only Fools and Horses (which still holds the British record for biggest sitcom audience, over 24 million for the 1996 Christmas episode Time on Our Hands). Set in 1960, this focuses on the family's early years in Peckham, with Shaun Dingwall as bone-idle Trotter paterfamilias Reg, Kelly Bright as his wife Joan and James Buckley as a youthful Del Boy. Nicholas Lyndhurst (who played Rodney in the original Only Fools), though, is the undoubted centre of attention in the role of Freddie "The Frog" Robdal, a charming geezer-about-town whose roving eye has settled on the lovely Mrs T...

John Sullivan's 90-minute prequel to Only Fools and Horses turned out to be the wonderful surprise of the week. With no laughter track and a minimum of slapstick, it is very different in tone to Only Fools and Horses. Rather than going for broad laughter, it concentrates instead on an affair between the unhappily married Joan Trotter (Kellie Bright) and a local crook (Nicholas Lyndhurst) fresh out of prison. It is a simple and touching love story played out against the backdrop of a pre-Beatles Britain, when money was short and the chance to move into a high-rise tower block was seen as the epitome of luxury. Helped by a strong supporting cast that includes Phil Daniels and Shaun Dingwall, Rock & Chips works on its terms, and will explain much about why Del and Rodney turned out the way they did.