Last Tango In Halifax (BBC1) has been praised for its sympathetic portrayal of an elderly couple in love.

In its first series, Alan and Celia, former childhood sweethearts, were reunited through the internet and found themselves finally able to enjoy a full relationship. Critics, and even some old age charities, singled the series out for praise for showing a man and woman in love in their old age without resorting to making it patronising or sentimental.

Tonight, Last Tango began its third series and I wondered whether it'd still be trading on its novelty of 'old people in love'. Surely the relationship has been established? Alan and Celia have already had two series to show they're headstrong and sincere, and not to be deterred by the misgivings of any of their troubled children or wayward relatives. Series 3 would surely branch out beyond the central couple's relationship?

I hoped it would, so was disappointed to see the episode opened with…an elderly couple in love. Alan and Celia were in a cosy restaurant, sharing a candlelit meal. They gazed fondly at one another. Alan told a saucy joke and Celia giggled.

So I was doubtful. There had been lots of fanfare surrounding Last Tango's return, but it just seemed to be retreading old ground, but with all dramatic tension leached from it. The couple are together and they're secure and in love. We know this, so why reinforce it with soppy romantic meals?

Then the rug was whipped from under my feet. The scene changed to a different restaurant. Someone else was having a romantic candlelit meal. This time it was Gillian, Alan's daughter. She had been invited to dinner by a local man who was good-looking and charming and she could hardly believe her luck. Then her hope died when he awkwardly revealed it was not actually a date he wanted but a serious and rather upsetting conversation over dinner. He thinks he may be her half-brother. Gillian was horrified. If this was true then her nice old dad, Alan, must have cheated on her mother.

We moved to yet another romantic scene. Caroline, Celia's daughter, was snuggled on the sofa with her partner to whom she proposes. But her partner is a lesbian, and also a black woman, both of which are unusual in Yorkshire so their own romantic dreams may be in for some shocks, and indeed we saw the first stirrings of trouble when some boys at Caroline's school engaged in homophobic abuse against the couple.

So we had three romantic scenes to open the series, none of which were what they seemed. Just as you may have been relaxing into the romance, we found that we weren't getting candles and fairy lights - despite all three scenes being heavily decorated with both - but news of a secret love child, deception, romantic rejection and the struggle against homophobia. Last Tango is not content to settle on Celia and Alan but opens out into the lives of their children and grandchildren.

With the various affairs and revelations Last Tango could almost sound like a trashy soap opera, but the dialogue keeps it from straying off into such silly territory. There are long, satisfying scenes of natural, earthy dialogue, delivered in unmistakable Yorkshire tones. It's a far cry from the shrieking Eastenders lingo of 'leave it! 'E's your bruvva!'