Alison Steadman is the mother-in-law from hell in the Yonderland Christmas special

But as the Christmas episode sees a monster called Chompus eat all the presents in Yonderland, and as the Elders call upon Debbie to help their children win the annual song contest at Thanktival, Barbara will find herself on a drunken adventure of her own – unbeknownst to her oblivious husband.

The Gavin & Stacey actress told RadioTimes.com: "She arrives with all the Christmas presents, and she's completely insensitive and over-the-top in every way. Not in any way malicious, she's not a horrible mother-in-law – but she she takes over the house as soon as she arrives, and it's basically all about her.

"She just wades in over her daughter-in-law, and she really likes a drink, so as soon as she gets there it's a large gin and tonic. And the husband's going, 'Oh nooo god don't.' Her husband (Anthony Head) is long suffering, a quiet man who just lives with this outrageous woman."

So will Barbara be making a visit to Yonderland? Steadman's not telling.

"Aw, now. She's in the real world, and I can't say what happens about Yonderland and all that," she teased. "That's for the audience to watch on the day. I can't say."

The surreal sitcom is written by its stars, Mathew Baynton, Simon Farnaby, Martha Howe-Douglas, Jim Howick, Laurence Rickard and Ben Willbond, and is directed by Steve Connelly.

Steadman, 70, said she was stunned by the sets and costumes and puppets used to create Yonderland.

"This is something so different and so special that it was such fun when I had breaks, and I'd just wander round looking at this amazing set and all these amazing costumes, and prosthetics that people had," she recalled.

"People are just transformed over and over again. And it is just an amazing thing to be part of, because I'm so used to doing dramas or comedy where it's all based in reality. But suddenly, I was walking round these amazing sets and as I say in make up just looking around the room at the transformations that were happening, it was just incredible. Really incredible."

And will we be seeing any more of Barbara?

"Well she's the mother-in-law, isn't she?" Steadman pointed out. "She could make a comeback, now let's never say never. I'd put the green frock on again and do it."

Watch out, Debbie...

The Yonderland Christmas special will air on 24th December at 6.30pm on Sky 1