The fly-on-the-wall mockumentary has surely run its course, but Trinny and Susannah: From Boom To Bust, succeeded in finding a little life left in the format.

The show followed the celebrated fashion counsellors and bosom gropers as they struggle to arrest a potentially terminal career decline. We witness a lucrative advertising contact fall through, their agent desert them, publicity stunts backfire catastrophically and their appearance at a golf convention fail to generate interest in their anti-fat underwear range.

Vanessa Feltz, David Furnish, Lulu and Prince Edward - I kid you not - are amongst the luminaries featured in supporting roles, but the programme stands or falls on Trinny and Susannah's performances, and they are pitch perfect. The pair pull off the difficult trick of playing the comedy whilst maintaining authenticity, and what could so easily have descended into self-indulgence proved a funny, poignant and strangely moving portrait of friendship in adversity.

Trinny and Susannah aren't in the same class as Nigella, more superannuated teenagers veering between strop and sulk than racehorse. But they're out of the same stable: they don't need second names; they're posh, of a certain age (46 and 48 respectively) and made their names on TV. They've also turned themselves into brands, and "do" humour, brilliantly. Readers might remember their fashion column in The Daily Telegraph's Weekend section, which, love it or loathe it, was a must-read for years. They took off into the fashionista stratosphere immediately afterwards with their TV series What Not to Wear, bullying members of the public into makeovers.

From Boom to Bust took up the story from there. It was a glorious spoof fly-on-the-wall documentary following the supposed collapse of their career. During this exquisitely funny offering, where small-screen setback was treated with the high seriousness of a Greek tragedy, every element of their career was mercilessly parodied.

We saw Trinny in a bath, covered in a hideous white facemask complacently discussing her diary. Cut to a taxi, where she was moving her colonic irrigation appointment so it would come after her "arse-slapping" slot with her masseuse (Think about it").

Cut to lunch with their agent, who told them not only had they failed to win a huge contract, but he was dumping them, too. Media names and celebrities appeared, as themselves, to mourn their decline: Dylan Jones (GQ editor), Lulu, David Furnish, DJ Neil Fox...

It got much worse, and much funnier. On to a golf and tennis trade show to promote their "magic knickers". "Susannah has a bit of a wobbly tummy," Trinny told the bystanders who had wandered up to their stall, hoiking up Susannah's dress to show how the magic knickers (deeply unflattering, flesh-coloured efforts) worked. Which is exactly the type of indignity they put their stooges through in their various makeover shows.

Will they, won't they climb back into the media spotlight? Perhaps they should get a makeover by Nigella. Now there's a thought.

Earlier this summer, fashionistas Trinny Woodall and Susannah Constantine posted a series of spoof films on the internet about their supposed attempts to get back on TV. A mixture of improvised and scripted scenes, spattered with F-words, they've been edited into a one-off comedy. It's supposedly modelled on Curb Your Enthusiasm, but at times the screaming and swearing make it more like something a group of drunken and/or stoned students would produce. That said, you have to admire them for mercilessly poking fun at themselves. "We used to be huge," screams Trinny in-between colonics, while Susannah spends most of her time in a cigarette- and alcohol-fuelled haze. It's fun to star-spot too: Lulu, David Furnish, Neil Fox and even a bemused Duke of Wessex make an appearance.

Trinny and Susannah - remember them? The telly fashionistas were all the rage a few years back, only to fall into relative TV obscurity after an invasion by an army of new clothing experts, captained by Gok Wan. They're back tonight though, but rather than doling out clothing advice to Britain's worst dressed, they send themselvs up in this spoof film that's more like Curb Your Enthusiasm than The Clothes Show. You've got to applaud the pair for mercilessly mocking themselves, and keen eyed viewers will spot cheeky cameos from the likes of Lulu and David Furnish.

Remember Trinny and Susannah? They were all the rage at the turn of the century - mauling women's breasts and telling them to wear proper bras. A money-spinning move to ITV followed, no one watched, Gok Wan became the nation's new makeover supremo and they've been quiet ever since.

Until now. Trinny & Susannah: From Boom To Bust (C4) was a spoof doc that acknowledged the duo's slump into TV limbo - charting their antics as they're dumped by their agent and try to get another programme deal. The mockumentary is a well-worn format and we'd seen it all before, the David Brent-esque faux egomania, tantrums and the attention-hungry celebs making random cameos.

There were several laughs to be had, though. Susannah showed a natural talent for playing a mentally unravelling borderline alcoholic and there were amusing digs at their showbiz chums. When, after losing a Cilit Bang advertising deal, the pair are seen crying in a shed, Trinny greets the news that David Furnish is popping round with an exasparated: 'Could this day get any f***ing worse?'

Meanwhile, their supposed new shows, Walk Tall With Trinny And Susannah, in which they made over jockeys, and Get A Leg Up With Trinny And Susannah, in which they found 'real-life unemployed people' jobs, nicely satirised the increasing desperation of TV documentary formats. It was a fun way of raising their profiles but difficult to see where it was leading. Is TV ready for a genre-mangling mockumentary makeover series? Stay tuned!