David Chater

A slightly sinister man (Reece Shearsmith) acts as the host of a séance. He ushers an innocent young girl into a stuffy room filled with Victoriana and then introduces her to Madame Talbot the medium (Alison Steadman).

Madame Talbot is shrouded from head to toe in black. Her eyes are white with cataracts. She carries one of those spooky dolls with an ivory face that she treats as if it were a real child. Spiritualist vapour pours out of her mouth like mist from an electronic cigarette, and while the lights flicker her voice alternates between a sweet little-odd-lady squeak and a diabolical, growl. And that is as much as I can say for fear of being savaged by a blue dwarf.

Although every single episode in this series is completely different, somehow Messrs Pemberton and Shearsmith manage to score one bullseye after another. In tonight's episode, a stressed-out daughter (Claire Skinner) invites her mother (Elsie Kelly) over to celebrate her 79th birthday party. The other guests are an alcoholic sister (Lorraine Ashbourne) and her appalling husband (Reece Shearsmith), and it degenerates into the birthday party from hell. And while the inferno is raging all around her, Granny sits there smiling, endlessly reciting the joke on her birthday card or playing games on her granddaughter's iPad. Imagine a more twisted version of Abigail's Party.

John Morton's affectionate satire of the inner workings of the BBC makes a welcome return. It has been accused of failing to go for the jugular, but that was never the intention. It's not about attacking the BBC, just as Twenty Twelve wasn't about attacking the Olympics.

According to Hugh Bonneville, it could just easily be about the NHS or Whitehall. "It's about satirising management structure and management speak," he says. W1A has two obvious and outstanding qualities. The first are the characters, all of whom are hideously recognisable and superbly performed.

Jessica Hynes steals the show as the grotesque PR supremo Siobhan Sharpe, but nobody in the ensemble cast puts a foot wrong. My personal favourite is Neil Reid's Controller of News & Current Affairs played by David Westhead, but there's a gem of a performance in tonight's hour-long episode from Andrew Brooke as the BBC's incompetent head of security.

It's other great quality is the dialogue, which sounds so natural that it feels improvised. Not so. "Every um and er - every odd word you hear - is there intentionally," says Bonneville. Because of this, the cast have to rehearse like an orchestra to get the rhythm right. "You spend your entire day running lines, running lines, running lines," says Bonneville.

Having produced two small masterpieces in a row, Steve Pemberton and Reece Shearsmith have set an impossibly high standard for themselves and it's only fair they should be allowed a breather. In tonight's episode, a volunteer (Pemberton) has joined a Samaritans-type call centre called Comfort Support Line. "Whatever the caller wants to talk about," says his boss (Shearsmith), "we offer active listening." There are two volunteers (Jane Horrocks and Nikki Amuka-Bird) who loathe one another, and the boss may be more disturbed than any of the callers. It's a promising set-up, but the episode doesn't unfold with the same simple, logical elegance as others in the series.

Tonight's macabre tale is totally different from anything that has gone before in this series, but it is equally accomplished and very, very funny. In an inspired pastiche of a 17th-century witch trial, Sir Andrew Pike (David Warner) has summoned two of England's most notorious witch finders, named Mr Warren and Mr Clark in tribute to the late actor, to try a defenceless old woman (Ruth Sheen) accused of consorting most lewdly with the devil. "Let us at least hear the testimony of the poor old crone," says Clarke, "before we reward ourselves with gold for burning her to death." It's like a long-lost Monty Python sketch, only better.

Steve Pemberton and Reece Shearsmith are something else. In the first series of Inside No. 9 last year, there was an episode involving a couple of masked idiots trying to steal a painting from a modernist home in which scarcely a word was spoken, and yet it was one of the funniest, cleverest, most imaginative and original programmes shown on television in the last 15 years. They've done it again.

This magnificent episode [The 12 Days of Christine] is not entirely perfect - there's a lot of spooky creeping around at night with lights flickering on and off that suggests the pair may have spent more time with The League Of Gentlemen and Psychoville than is strictly healthy. However, if you treat the presence of the otherworldly as a means to an end, the episode is a distillation of accurate observation that says more about the hope and messiness and disappointment of life in half an hour than most dramas say over an entire series.

It describes the trajectory of one woman's life - superbly performed, as always, by Sheridan Smith - from her student days to marriage, children and beyond. At the very end, looking back with sadness and regret, she says: "I didn't think it would turn out like this." There is something infinitely poignant about seeing two different versions of events and recognising the chasm between what might have been and what was.

The dark imaginations of Steve Pemberton and Reece Shearsmith are back with six more self-contained, bleakly comic dramas set in different locations, all of which have a No 9 on the door.

Tonight's opener has echoes of the very first episode of all, in which a diverse assortment of characters at a country house squeezed into a cupboard during a game of sardines. The difference here is that the characters - an anally retentive doctor, a flatulent German, a British couple on the way to their daughter's wedding, a rude Australian backpacker et al - squeeze into a tiny couchette on a train out of Paris. You may think you know where it is headed, but don't be so sure...

Its hard to know which to admire more - the rich and perverse imaginations of Steve Pemberton and Reece Shearsmith, or the range of acting talents that has brought this strange and memorable series to life. The final episode is also the most Gothic. A sensible young woman goes to babysit in a refrigerated mansion while its owners, a most unusual brother and sister played by Shearsmith and Helen McCrory, are called away on an urgent matter. Upstairs lurks a bedridden brother who was born inside out. The story is called The Harrowing, named after Christ's descent into Hell to free imprisoned spirits. Babysitting doesn't get tougher than this.

Quality attracts quality. Reece Shearsmith and Steve Pemberton have developed such a track record over the years that many of the finest actors in the country jump at the chance to appear in their dark imaginings. And the pair are never predictable. You might think you know where they're heading, but then suddenly they veer off in an entirely different direction. The episode tonight, set in a West End theatre, appears to be a re-working of Macbeth, with Macbeth's understudy (Shearsmith) being egged on by Lady Macbeth's understudy (Lyndsey Marshal) to seize the crown. "This is your chance" she says. "All you have to do is take it". It's not quite that simple.

Steve Pemberton and Reece Shearsmith focus their demonic gaze on celebrity worship and human greed. Tamsin Greig runs an outfit that makes dreams come true for sick children. If a little boy with cerebral palsy wants to play chees with Noel Edmonds, she will organise it. Here she arranges for the pop star Frankie J Parsons to come to the birthday party of a terminally ill little girl. After blowing up a balloon, he keels over - and the balloon filled with his dying breath is worth far more than the kidney stone sold by William Shatner for $25,000. "That's sick!" explains the appalled mother (Sophie Thompson). "The world is sick" replies her husband (Pemberton).