Derek Jacobi and Anne Reid return in Sally Wainwright's simply excellent family saga. Celia is overjoyed when Alan regains consciousness after the heart attack. And for a brief moment it's all happy families as both clans unite over the good news. But soon, Gillian purges her guilt over her night with John and the foundations quake anew. Every moment feels like truth thanks to a script so tightly woven you could strain tea through it. Such acting, such writing; it's as near to perfect television as you can get.

At the end of the first series of Sally Wainwright's winning, warm-hearted drama, dear Alan was hovering between life and death after a heart attack. Obviously he survives, or there wouldn't be much point in returning to Yorkshire for a second helping.

It's great to see everyone again in a drama where pensioners are loved, cherished and never dismissed as inconvenient, and this time the masterly Wainwright has broadened the drama to dig deeper into other characters, notably Caroline (Sarah Lancashire, who's excellent) the newly-confident and newly out lesbian. While Alan and Celia (Derek Jacobi and Anne Reid) mend the relationship that almost fractured for ever, there's a shift in the tectonic plates in the romantic lives of their families. Just look at poor Gillian (Nicola Walker), who is made to pay for her terrible mistake in sleeping with John (Tony Gardner), Caroline's pathologically hopeless estranged husband. No one does bleating wretchedness like Gardner - no one.

Last Tango in Halifax (BBC One) was very simply plotted, although, in contrast to a drama like The Town, writer Sally Wainwright's dialogue tended towards the emotionally incontinent.

"Why can't you accept that I want to be with Kate, that I am old enough to make my own decisions, and to accept it and be civilised about it?" wailed Sarah Lancashire's lesbian headmistress Caroline as she tried to drag her mother Celia (Anne Reid) into the 21st century.

A few scenes later and Celia had had a change of heart, declaring that she had "played hardball long enough" (perhaps the only 75 year-old in Britain to have ever used that term) and was ready to accept her daughter "for who she was" having been "on the road to Damascus".

Last Tango in Halifax was sometimes silly and two episodes too long. But it was that difficult beast, a comedy drama, and for all its faults could sometimes be both funny (any scene involving Tony Gardner as John, Caroline's feckless, needy ex-husband) and dramatic (any scene involving Derek Jacobi's Alan).

Pensioner Alan's late-blossoming courtship of Celia, his first love, was touching and the power came from Jacobi's understated performance. This theatrical knight has played many fascinating, complex men (Richard II, Francis Bacon, Alan Turing) but I have never seen him play ordinary. Often, great actors fail when they try to be the everyman; thwarted by their own heavyweight presence. But Jacobi as Alan achieved much by doing very little. Just by sitting in front of the Aga and sipping his tea thoughtfully, he vividly portrayed a kind, unremarkable man who had looked at life from atop his West Yorkshire farmhouse, and after three quarters of a century, had worked out its deepest mysteries. Amid the drama's silly theatrics of cheating spouses, concupiscent toyboys and alcoholic screw-ups, Jacobi added some much-needed depth.

The series has been a ratings success and will return next year when the grand and sometimes unlikeable Celia will prepare to walk down the aisle to The Entrance of the Queen of Sheba. Let's hope no pesky TV producer introduces an unfathomable story arc that will prevent her from getting her wish.

A second series has already been commissioned, which means that this is actually The ­Penultimate Tango In Halifax.

And if that makes things a little awkward, that's nothing compared to the dinner party which forms the backbone of tonight's episode, where you could cut the ­atmosphere with a blunt spoon.

And although, like pensioners driving over the Pennines in the dark, this series might have lost its way a little around the middle, tonight's finale is an absolute triumph.

The cast, led by Derek Jacobi, Anne Reid, Sarah Lancashire and Nicola Walker, have done Sally Wainwright's fabulous script proud, making these characters you can believe in even when they're behaving appallingly.

In fact, especially when they're behaving appallingly, as Celia and her daughter Caroline do tonight.

Tears, laughter and truthfulness are all here in abundance.

Last week Celia was informed that Caroline was in a relationship with another woman - a fact you might have thought had been plonked into the story simply to spice things up a little.

After all, as one character remarks tonight: "It's nowt these days. Nobody bats an eyelid."

On the contrary. The way Celia reacts to this news makes Alan see her in a whole new light.

Geographically they might not have travelled very far in the 60 years they've been apart, but Alan realises he should have been warned by Celia's choice of daily newspaper that there's a huge gulf between them in attitudes.

Let's just say that if only Celia read the Daily Mirror, so much unpleasantness might well have been avoided.

Having learnt that her daughter Caroline is a lesbian, Celia is shocked and judgemental. "What will folk think?" she demands of her fiancé, Alan. They'll be "pointing and saying things".

As Sally Wainwright's clever, multilayered drama ends, what started out as the most dreamy of courtships appears to have hit some very choppy waters when Alan (Derek Jacobi) decides he doesn't like this new side to Celia (Anne Reid). Caroline (Sarah Lancashire) isn't enamoured of it, either: "You're going to die lonely and bitter," she yells at her mother when the pair trade cruelties in a terrible row.

I'm going to miss Last Tango in Halifax, as will presumably its huge BBC1 audience. It was one of those dramas that arrived out of nowhere to an instant embrace from viewers, and none of us will quite be able to let Alan, Celia, Caroline and Gillian get away from us.

By the way, you will cry at the end. Oh yes, you will.

Gentle doesn't always have to mean trivial, as Sally Wainwright's charming, surreptitiously incisive drama approaches its final episode (at least until it returns next year). Derek Jacobi and Anne Reid's smitten pensioners continue to be far more functional than their midlife crisis-ridden children, who are finding matters off the heart rather more challenging. That said, secrets lurk even in the histories of this apparently untroubled couple, as Alan opens up about Eddie's suicide and Caroline prepares to reveal something certain to test Celia's prejudices. For all the bad behaviour and human frailty on display, the total absence of mean-spiritedness or passing of judgment makes a happy ending tomorrow (at 9pm) almost inevitable. As adept a balance of humour and sentimentality as you'll see this side of Call the Midwife.

The conclusion of writer Sally Wainwright's excellent, if increasingly bonkers, second-time-around comedy drama. Dismayed by the harsh reaction of Celia Dawson (Anne Reid) to the revelation that her daughter Caroline (Sarah Lancashire) is gay, Alan Buttershaw (Derek Jacobi) calls off the wedding, leaving a distraught Celia to face her demons. Has she lost her soulmate all over again?

Sally Wainwright's tale of an old flame rekindled after 60 years is beautifully written and acted, and it moves along at an engagingly ungeriatric clip. Following last week's adventure Alan (Derek Jacobi) and Celia (Anne Reid) are in high spirits, and events have emboldened their daughters Caroline (Sarah Lancashire) and Gillian (Nicola Walker) to move on with their lives. But then Caroline reveals her plans to her feckless husband. Fans note: the final episode is tomorrow.

Now that Alan and Celia have accidentally been shut in a stately home, their anxious families can have a long, difficult and revelatory night as they wait for news.

It's a ridiculous plot device, but at least it allows daughters Caroline and Gillian to reach an understanding as they are locked together by worry.

As for the two elderly lovebirds (Anne Reid and Derek Jacobi), they are oblivious to the ructions back in Halifax and Harrogate, and are happily planning their future together as they play cards by candlelight. Then suddenly things get all Secrets of Crickley Hall when they hear a ghost...

It feels like a turning-point episode in Sally Wainwright's drama, when we learn more about the sorrows of the past, and everyone, particularly Caroline (Sarah Lancashire), decides it's time to seize some happiness.

"We're not burglars, we're pensioners," cries Celia (Anne Reid), spooked by the creaks and groans of Southowram Hall where she and Alan (Derek Jacobi) remain locked in. Their families are frantic over the couple's whereabouts, but the panic brings their respective daughters closer together and a tentative friendship is formed. Sally Wainwright's comedy-drama has charm in abundance, its chief joy the pairing of Reid and Jacobi, particularly delightful in tonight's episode when they spar off each other over a candlelit game of cards.