I've seen a few things in the Playhouse Presents series. A bit like going to slightly up-its-own-arse arty theatre (only with big name stars). In my house we've chortled loudly, not because we've thought something was funny but to show we've recognised it as a joke. And in the advert break we've rushed to the kitchen to down a couple of pre-poured and now warm glasses of white wine, after which the second half has been more bearable and passed faster.

Psychobitches, though, which piloted last year, flies past, and is genuinely hilarious. The idea - famous people from history visit a modern-day therapist - isn't entirely new, I don't think (perhaps you can think of the examples: I can't). But it's written, by a vast team of writers, with such originality and wit, imagination and cojones, that it feels like a whole blast of new. In my house at half-time, and again at the end, we were comparing, and reliving - and relaughing at - favourite bits and characters. A nightmarishly needy Audrey Hepburn; Bette Davis and Joan Crawford bitching and backstabbing and bashing each other over the head with their best actress Oscars (it manages to be both clever and silly, a very attractive combo); Margot Fonteyn being very very old; Jacqueline du Pré communicating only through her cello, expressing love, childhood, adultery, coriander (a mournful downwards glissando, perhaps to signify distaste, or wilting?).

My highlight is Julia Davis's Sylvia Plath, but a Sylvia Plath who deals with all her internal strife and angst by adopting the persona of fellow poetess ... Pam Ayres. Davis as Plath as Ayres: it's a mash-up from heaven. Sharon Horgan's delusional, egocentric, megalomaniacal Eva Peron is also a joy, sipping her boobles (champagne) and naming leedle seedies in Argentina after herself, who she refers to in the third person. And the puppet-sized Brontë sisters, coarse Yorkshire slags squabbling on the sofa, mainly about (not) losing their virginity. "It's not me who's the desperate one," Charlotte squawks to Emily. "I'm not the one gagging for it that much her fanny's frothing like a beck in a storm."

So many highlights in fact, and such great performances, from the aforementioned, and from Sam Spiro, Katy Brand, Frances Barber, Sarah Solemani, Zawe Ashton, Jo Scanlon and more. Not forgetting Rebecca Front, as the kind, deadpan, calm (mostly: Audrey pushes her), but also human and very subtly arch therapist. "What do you have?" she asks politely, after Nina Simone has soulfully wailed: "Ain't got no home, ain't got no shoes, ain't got no money, ain't got no class ...". The answer? Depression of course.

They all seem to be having such a brilliant time doing it, it's impossible not to get swept along in the tide of fabulousness and sharp writing and cleverness-meets-silliness, with just a pinch of coriander lunacy. This is very funny women at their very funniest. Oh, plus one man, Mark Gatiss as Joan Crawford, also lovely.

Step up Psychobitches (Sky Arts 1), which started out as a pilot last year but has now deservedly bloomed into a full series.

The set-up is simple. Rebecca Front, understandably striking while her iron is hot, plays psychiatrist to a succession of celebrity patients - of a decidedly retro vintage - which is basically an excuse for a host of top comic talent to show off in a series of over-the-top impressions.

In the space of 25 minutes or so, everyone from the Brontë Sisters to Margot Fonteyn by way of Nina Simone had a go at hogging the ego-crazed spotlight.

The quality control is variable but when Psychobitches is good, it's very, very good, with Samantha Spiro, a world away from her mousy turn in Grandma's House, absolutely fabulous as an infuriatingly kooky Audrey Hepburn.

Even better was Julia Davis turning chirpy Pam Ayres and tormented Sylvia Plath into a poetic double act, chipper rhymes morphing into angst-ridden soul-searching in the blink of a couplet. Delightfully bonkers.

You could be forgiven for thinking that Psychobitches, Sky Arts 1 new comedy series, is an all-female affair. It isn't, though nobody gets on screen without dragging up, the essential conceit being that the patient list for Rebecca Front's psychotherapist is composed entirely of famous women from history. Some of them have come to do some work on a family relationship, such as the Brontë sisters, bickering furiously in a row on the couch.

Others are working on more private problems, including Audrey Hepburn, who is having difficulty finding the fine line between being charming and infuriating. And it's very funny. As Hepburn, Samantha Spiro is terrific, winsomely inviting Front's weary therapist to play imaginary ping-pong. But Julia Davis is good too as Sylvia Plath, who excitedly confides that she's been experimenting with writing in a different persona: "Oh I wish I'd looked after me toes/ Not treated them like they were foes," she reads perkily, before black despair gradually edges out Pam Ayres.

The writing is often excellent - Charlotte Brontë's furious complaint that her oversexed sister is "frothing like a beck in a storm" seemed oddly plausible - and even the spaces between the sketches are drily funny (Jeremy Dyson directs). But it would be unfair not to give due credit to a performer who could easily get overlooked, since she's the foil and not the funny woman: Rebecca Front gets bigger laughs doing virtually nothing here than some of her co-stars do with a string of punchlines.

Unfortunate title aside, Psychobitches is a wonderfully original idea - what if famous women through the centuries were alive today and seeking treatment from a psychotherapist? In a quasi-sketch format using the talents of 10 credited writers, it's a neat construct that allows writers' imaginations free rein, unconstrained by time, place or actual facts, and gives a roll call of talented actresses (and the occasional bloke) a chance to do their very best impersonations.

Last night's opener of a five-part series (expertly directed by The League of Gentlemen's Jeremy Dyson) started with Rosa Parks, not on the couch but "here for my appointment" in a glorious blink-and-you'll miss-it sight gag, where all the other women in the waiting room jumped up to offer her their seat. Actually being therapised, as it were, in the Sigmund Freud-style office, were (among others) an irritatingly winsome Audrey Hepburn (Sam Spiro), a grandiose Eva Peron (Sharon Horgan) and a self-obsessed Sylvia Plath (Julia Davis).

Plath was trying out a new writing persona in which she donned her grandmother's dress and wig and morphed into Pam Ayres - "I wish I'd looked after me toes/ Not treated them like they were foes" - one of many moments in this half-hour when I laughed out loud. It was an inspired gag. Equally good were the scenes involving the bickering Brontë sisters; Anne (Sarah Solemani) was meek but knowing, while Charlotte (Selina Griffiths) was withering about Emily (Katy Brand) needing to lose her virginity, or, as she put it in her broad Yorkshire vowels, "She should fuck off to Keighley on a Friday night and lose it to a cowhand and do us all a fucking favour."

Among the mix was Mark Gatiss and Frances Barber hamming it up marvellously as Joan Crawford and Bette Davis, in full What Ever Happened to Baby Jane? mode, endlessly outdoing each other in the meanness stakes, while Rebecca Front's therapist - an unshowy part that could easily go unnoticed in this parade of misfits - was nicely pitched. There was the occasional miss, but overall this was a joy.

An amazing lineup of comic actors have a ball playing historical figures in therapy opposite Rebecca Front's ever-patient psychologist. Julia Davis puts a new twist on the poetry of Sylvia Plath. Samantha Spiro is a ping-pong Audrey Hepburn, Mark Gatiss a superb Joan Crawford to Frances Barber's inspired Bette Davis. Katy Brand stars as one of three sweary Brontë sisters. It's the comedy equivalent of eating a lot of biscuits. If you miss it you will forgo the funniest thing on TV this year.

Rounding off the Playhouse Presents... series, this five-part comedy sketch show makes itself comfortable on the couch for a witty variation on the therapist theme of HBO's In Treatment. Rebecca Front anchors the action as a long-suffering psychoanalyst whose appointment diary is lit up by a galaxy of stars from yesteryear, as played by some of today's finest acting talent. Stand-out headcases include Frances Barber and Mark Gatiss as Bette Davis and Joan Crawford (in Whatever Happened To Baby Jane mode), Sam Spiro (Grandma's House) as irrepressibly cutesy Audrey Hepburn and Julia Davis (Hunderby) conjuring comedic magic by mixing poet Sylvia Plath's tragic angst with the simple jollity of Pam Ayres.

Psychobitches, stars Rebecca Front as a therapist whose patient roster consists solely of famous women from throughout history. Essentially an excuse for a fast-paced series of disconnected sketches, this simple premise is only semi-successfully executed by co-writer/director Jeremy Dyson from The League of Gentlemen.

Resembling a surreal parody of the great In Treatment, the series begins with a neat visual gag involving Rosa Parks - I suspect that's the first and last time I'll ever place those words in that order - before roaring into gear with Front's Grandma's House co-star Samantha Spiro delivering a pitch-perfect evisceration of Audrey Hepburn's irritatingly kooky screen persona.

Unfortunately, it then devotes far too much time to a mirthless series of Brontë sisters sketches - no, it wouldn't be hilarious if they were portrayed as gruff, foul-mouthed northerners - and Julia Davis as Sylvia Plath, which, while beautifully performed, hammers its one joke into the ground. Elsewhere, Frances Barber and a dragged-up Mark Gatiss (Dyson's League of Gentlemen cohorts crop up throughout the series) sell the hell out of a warring Bette Davis and Joan Crawford, but without banishing memories of French & Saunders' superior take on their feud. The only other sketch that really takes flight is Sharon Horgan as a glamorously self-obsessed Eva Peron.

As an excuse for a cast of talented, funny women to show off their versatility, Psychobitches is a success. But reducing Front to a straight role feels like a waste of her abilities, which merely adds to the overall air of mild disappointment.