After a two-year hiatus, the cast of Last Tango In Halifax is returning for a two-part Christmas special, but as Sarah Lancashire and Nicola Walker tell Susan Griffin, don't expect too much merriment

Sarah Lancashire's been on our screens for 30 years, but in all that time, she's never taken part in a Christmas special - until now. She and the rest of the Last Tango In Halifax cast, including Sir Derek Jacobi, Anne Reid and Nicola Walker, have reunited for two episodes of the Bafta award-winning drama.

It might be billed as a festive special, but don't expect cheery times around the Last Tango turkey. This is Sally Wainwright after all, the prolific writer behind the brilliant but grim Happy Valley.

"There's a lot of friction, it's not a cosy Christmas," confirms Lancashire, 52, who's taken refuge from the blistering chill in a nearby farmhouse during a break in filming.

"Every so often, we take a break from shooting and go [sings Shakin' Stevens'] 'Merry Christmas Everyone'. It's a break from the sobbing and screaming!" adds Walker, who's joined her co-star.

It's almost two years since the last series and as Lancashire observes, "That's a long time to be away from characters.

"At times it's felt a bit strange, but also, we're finishing in a week-and-a-half and we've only really just started. So that's quite odd."

The lengthy absence is reflected in the storyline.

As Walker, 46, notes, "They're all up against it and especially being around Christmas time, and that thing of Christmas putting extra pressure on the entire family. None of us wanted to come back and think, 'Oh yeah, it's just as it was and it's cosy'. They've got quite complicated things going on in all their lives."

Her character Gillian's still living and working on the farm, but is increasingly irritated by the fact her husband Robbie, played by Dean Andrews, "is making lots of changes and building stuff. She feels like someone's come into her environment," explains Walker.

Fans will remember Gillian was having doubts over their wedding at the end of the last series. Her feelings were complicated by the guilt she feels for killing his abusive brother Eddie, her first husband, and passing it off as a suicide, a secret she's only confided to Caroline (played by Lancashire).

It's only after some cajoling that she decided to go through with the ceremony at all.

"We said, 'You can just divorce him," Lancashire adds. "Marry today, divorce later."

"You might think that would've happened, but it hasn't," continues Walker.

"Although there's a scene early on where Caroline asks how it's been and Gillian realises that maybe everything isn't as great [as she pretends].

"Obviously she was very frightened that she'd be overcome with feelings of guilt [over the killing] and sits there and goes, 'No, no, I'm not,' and then you just see it percolate."

Caroline and Gillian have experienced something of a tumultuous relationship since their respective parents, Celia (Anna Reid) and Alan (Derek Jacobi), reunited decades after they were childhood sweethearts.

But Lancashire reveals, "they're in a very good place" now, "very united".

"Caroline's still her confidante and the only one Gillian talks to," adds Walker. "She's putting it all on her."

And that's despite Caroline facing her own dilemmas.

Shortly after exchanging vows in series three, Caroline's partner Kate was fatally injured in a car crash leaving a new born baby, Flora, to be taken care of. When we catch-up with Caroline, she's embarking on a fresh start, with a new job and home.

"And she sort of has an encounter with another woman," reveals Lancashire, careful not to give too much away.

"It wasn't anything she consciously set out to do, but she finds herself in a situation with another woman, which is quite interesting, because she's dramatically younger.

"She's a local woman who pursues Caroline, not the other way around, but Caroline isn't ready to date. She's still very much grieving for Kate."

It's not all doom and gloom however, with some much-needed respite in Alan and Celia's interest in the local am-dram group, and the latter's starring role in a production of Blithe Spirit.

Though the special's set to be one of TV's festive highlights, Lancashire won't be watching. "I'm usually in the kitchen all Christmas," she says. "And it's work, not a vanity project. If I do watch something, I tend to watch it alone and see how it's all come together. But it's never a joyful experience."

Walker won't be tuning in either. "I think it's worse at Christmas, if everyone's there and you go, 'Oh, come here everyone, I'm on!" she laughs. "That's just not going to happen."

A new series hasn't been announced, but the special leaves it open for us to return to their lives down the line. "It doesn't wrap everything up but we haven't really talked about it amongst each other, because we're all doing things, aren't we?" says Lancashire, looking at Walker.

"It's just nice to come together and do this. And because it's not a definitive end point in the story, it's open to that, certainly," says Walker. "If Sally wanted to do that, we'd all be jumping."

The two-part special of Last Tango In Halifax will air on BBC One on Monday, December 19 and Tuesday, December 20