Poor Angus Deayton has been dropped again. Rob Brydon steps into his shoes and very good he is too (much better than AD, who treated it as if he had somehow turned back time and was on the set of HIGNFY). Also good are the team captains: David Mitchell's natural habitat is the panel show and Lee Mack is naturally funny. Tonight's guests are Jo Brand and Russell Howard, providing back-up laughs, and Carol 'whaat now?' Vorderman and Larry 'do something about your son' Lamb are the straight men. It's never hilarious but it's always funny and less annoying than Mock The Week, so everyone should be glad to see it back.

Toilet humour. It isn't big and it isn't clever. But who cares when the brilliant Getting On, which I'm missing already, can turn the humble stool into a rich source of wipe-away-the-tears mirth?

This bleakly endearing geriatric ward comedy has only had a three episode run but richly deserves a full length series: with nurse Kim, sister Den and Dr Moore, writer/stars Jo Brand, Joanna Scanlan and Vicki Pepperdine have created an unforgettable trio. It helps, of course, if you like your potty humour wrapped up in a quilted loo roll of sophistication.

Taking revenge on neurotic meddler Dr Moore, Den decides to tamper with her precious report on patient faeces. A simple word substitution does the trick. 'What's another word for faeces?' queries Den. 'My youngest calls them plop plops,' offers Kim. Cue the following: 'The chart demonstrated construct validity for characterising stool function together with concurrent validity for characterising frequency of plop plops.' It cracks me up just typing it.

This, sadly, is the final episode of Jo Brand & Co's superlative series. Because it is based on mood, inflection and myriad flashes of acute observation, Getting On is almost as difficult to describe as a piece of music. Certainly there are headline events in each episode - tonight, for example, there is a "conflict resolution strategy meeting" and an argument about who won the raffle - but it's the interaction of the characters around these events that is so accurate and funny and wonderful. It is bound to be recommissioned; nobody would be mad enough to let something this good slip through the cracks. When that happens, I hope they continue to go for accuracy rather than leaning towards laughter, because it was the truthfulness that made it so extraordinary.

It's the final episode of Jo Brand's blacker-than-black comedy set on an NHS geriatric ward, and what a missed opportunity it has proven: only three episodes long and ferreted away on BBC4. Tonight, Brand's nurse Kim has to partake in a jargon-strewn 'conflict resolution strategy' after her bawdy humour hits a sensitive target, Den and Dr Pippa tie themselves in knots over who exactly has won the raffle prize (a hamper), and the stool research continues. Bleak but brilliant.

Getting On gets better. Somehow Jo Brand, Joanna Scanlan and Vicki Pepperdine have created a comedy about a modern NHS ward that is piercingly weird, coldly plausible, heartbreaking and hilarious. This week, a foul-mouthed racist OAP went on the rampage, delivering a bloody nose to the new male matron, who desperately tried to remember his stay-calm management training module as his nose bled.

The humour in Getting On is stealthy: the harassed doctor searched for her stool samples, hustled pathetically for a car-parking space and saw not that many patients - then looked at her lined face in the toilet and wondered where the years had gone. This moving reverie was interrupted by the head nurse rapping on the door, insisting that it should never be locked. The doctor she fancied, played by The Thick of It's Peter Capaldi (who also directs Getting On), looked past her at a much younger model. The comedy in Getting On is as wincing as The Thick of It, with the added pathos of near-death patients wheezing their last. Or not, as happened this week, with the sudden, vexing recovery of one.

Ward B4 is a backwater of the NHS, a place where old folks go to wither away and where the staff also look as though they have seen their best years. From this unremarkable setting, the three writer-actors - Jo Brand, Vicki Pepperdine and Joanna Scanlan - have created a gem of a comedy. They never overplay their hand, generally stay one step ahead and know that while a note of pathos is fine it still has to be funny. In this second episode, sister Den and nurse Kim have an abusive patient to deal with.

Set in a geriatric ward, naturalistically performed and filmed in a spartan, documentary style, Getting On might not sound the most inviting of comedies. Do not be misled.

Written by and starring Jo Brand, Joanna Scanlan and Vicki Pepperdine, Getting On is a gem of a show that somehow succeeds in being by turns cynical, compassionate, depressing and life-affirming. And funny. Did I mention funny?

Getting on: another reason to adore Jo Brand

What I particularly liked is that the humour has a purpose that isn't simply the sound of its own cackling. It's potentially as good and barbed as The Thick of It.

One of the clues to successfully turning an in-joke into an out-joke is to trust people to get it without too much signalling. Getting On, a comedy set in an under-resourced geriatric ward, clearly understands this, beginning in a way so indifferent to the arrival of newcomers (us, watching) that you almost feel you should cough to let them know you're there.

Sister Flixter is sitting by an old lady's bedside, one hand checking her texts, the other clasping the patient's limp hand. The camera pans slowly to show a cake - "Happy Birthday Lily 87" - and then, without any fuss, it becomes apparent that Lily isn't going to be eating any of it. It's the kind of detail that might be played for cheap pathos in a different kind of series, but here - without a line of script - it very effectively delivers a key signature. This is a comedy about a place where the bleakly mortal and the banal are continually rubbing up against each other.

Sister Flixter didn't have much time to worry about Lily because a something distracted her, a coil of excrement discovered on a ward chair by Nurse Wilde (Jo Brand). To Nurse Brand, this is "shit". To Sister Flixter, it's a "critical incident", which will require the requisite NHS paperwork and to Dr Moore (Vicki Pepperdine), it is a "faecal deposit" and valuable raw material for her current research. For want of a stool pot the stained chair was pushed into an alcove behind hazard tape, where it is still odorously contributing to the ward's atmosphere of mismanagement when the new matron turned up later to add yet another chief to a tribe already short on Indians. That's the central joke of Getting On - of priorities and interests competing so effectively that virtually nothing gets done - though "joke" is too crude a word for the stealthy way in which the humour bubbles up through the cracks.

Written by its three leads and directed by Peter Capaldi, Getting On is in the tradition of The Office and The Thick of It, rather than Only When I Laugh or Green Wing. You can feel the grit of real events inside the comedy, such as the ludicrous attempt to translate the genial babblings of a patient speaking some unidentified Indian language (they discover she's been saying "I want to die. Please kill me") or the closing moment when Sister Flixter and Nurse Wilde found themselves having to mumble their condolences to Lily's sister, through mouths still filled with the dead woman's cake. And the most surreal gags turn out to be true. Dr Moore's strange obsession with the patient's bowel movements turns out to be the result of an ambition to "expand the Bristol Stool Chart from the current seven to an exhaustive 37 types of patient faeces". Wonderfully, the Bristol Stool Chart really does exist, a turd-spotter's identification chart that runs the fecal gamut from "hard lumps, like nuts" to "entirely liquid". Getting On doesn't feature on it anywhere.

The opening line of a comedy is crucial in setting the tone - it lets you know where the writers are coming from. So when Getting On dumped "there's a s*** on the chair" on us as an introductory gambit, it was clear this wasn't going to be an easy ride. That the words were squeezed from the lugubrious gob of Jo Brand, resplendent in nurse's uniform, only piled on the agony.

Yet I can't remember the last time I howled so loudly. Cut from the same downbeat naturalistic cloth as The Royle Family and The Office, Getting On mines the misery of a hospital geriatric ward for bleak laughs. Yet for all its pot-shotting at NHS bureaucracy and patronising consultants, there's a heartening thread of humanity that stitches this mordant little gem together.

You don't need to have spent any time in geriatric wards to get Getting On but possibly it helps. Director Peter Capaldi (taking time out from political jiggery pokery in Torchwood and The Thick Of It) gets the feel of washed-out light and weary resignation spot on; even the corridors feel like they're shrugging their shoulders and doing all they can to keep from falling over.

But where Getting On really scores is with the performances of its central trio of writer/actors. Brand is matched every cynical sigh of the way by Joanna Scanlan and Vicki Pepperdine as the lap dancer-booted sister and the stool-obsessed consultant ('what type is it?' 'I'd say type four: snake') around whom Getting On revolves in increasingly desperate circles. One heartbreaking, hilarious scene summed up. An Asian woman had been muttering away in her bed for an age and finally the nurses got a translation over the phone. 'What's she saying?' 'I want to die, please kill me.' 'Put it in her notes.'