‘Fungus the Bogeyman’: Victoria Wood and Timothy Spall on the new TV production of of Raymond Briggs' classic

Sitting in her trailer in a suburban municipal car park and sporting a very fetching curly blonde comedy wig, Victoria Wood recounts the most gruelling thing she has had to endure while filming Fungus the Bogeyman, Sky 1's big family Christmas drama – and no, it's nothing to do with the wig.

Tom MacRae's three-part adaptation of the classic Raymond Briggs children's story, which begins on 27 December, charts the difficulties experienced by a grime-smeared renegade family from the slimy, subterranean realm of Bogeydom.

The family of gunk-loving jolly green giants – the dependable Fungus (Timothy Spall), his loyal wife Mildew (Joanna Scanlan) and their errant son Mould (Haydon Downing from Runaway) – run into trouble when they become trapped in the world of humans, known to the Bogeys as “Dry Cleaners”. Their problems are compounded when they are forced to live undercover in the (to them) hideously sterile world of suburban Daventry.

Wood, 62, plays Eve, a Dry Cleaner who takes in Mould but may not be all she seems. She recalls: “One scene was particularly painful to do. Mildew can't stand the lovely kitchen she has in her new house in Daventry. So she tips the bins from the street all over the kitchen, spreading dog poo over the floor.

“Meanwhile, Fungus, in an utterly repellent pair of Y-fronts, is daubing the walls with slime. We were doing that scene in a boiling hot kitchen for two days, and it absolutely stank! It was not terribly glamorous, but it will be very funny.”

The Bogeys revel in squalor and abhor cleanliness. They cherish flatulence above all else – their motto is, “I stink, therefore I am” – and their favourite book is “Anne of Green Bogeys”.The walls of Bogeydom are plastered with posters proclaiming slogans such as “Soap is your enemy” and “If it ain't broke, break it”. Their fruit markets sell the Bogey delicacy of rotten apples crawling with maggots. Meanwhile, one of Mildew's favourite dishes is a freshly filled baby's nappy.

The Bogey family's tribulations begin when the good-natured young Mould starts to tire of his life being perennially grungy and scaring “Dry Cleaners” every night. He longs to leave behind the festering world of Bogeydom and discover more about the apparently enticing hygienic human life on the surface. He is becoming – shock, horror – “Dry-curious”.

When Mould makes a bid for freedom, he is chased on to the surface by his loving yet over-protective parents. But unfortunately, all three Bogeys become marooned in the human world and have to attempt to fit in among the meticulously mown lawns and impeccably clipped privet hedges of suburban Daventry – with monstrous consequences. They particularly struggle to understand their respectable human neighbours, Wendy (Keeley Hawes) and Daryl (Marc Warren).

Taking a break from a hard morning's “Bogeying”, Spall comes over to chat. He reflects that in spite of their passion for all things putrid, the Bogey family are essentially good-hearted characters who possess the trademark Briggs quality of decency.

“Yes, Fungus, Mildew and Mould are monsters and have these despicable habits. They are these farting, bogey-eating creatures, but they are also these rather mundane, slightly Edwardian characters,” he says.

“The Bogeys don't want to upset the neighbours, but they can't help it. To them their idiosyncrasies are normal, but to others they are quite unacceptable. ”What is lovely is the juxtaposition of the unseemly, the unsavoury and the disgusting with these really kind, sweet, ordinary souls. The Bogeys are disgusting, but they're also very decent.“

It is true that Briggs' story, which was first published in 1977, continues to strike a chord because as well being a heartwarming tale about the enduring power of family love, it is also a celebration of the subversive.

Spall, 58 observes: “Fungus the Bogeyman is not conventional. The savouring of the unseemly must be encouraged in the next generation. That combination of warmth and unsavoury-ness must live on.”

That sounds like a campaign slogan. “It might be the answer to a lot of problems, yes!”

Scanlan, 54, was also taken by the Bogeys' commendable desire always to do the right thing. “I read Briggs's book Ethel and Ernest, which I really think is wonderful. It is the story of his parents. I very much tried to model Mildew on his mother. I think Briggs is writing about his parents in the values he gives to the Bogey parents.

“There is a modesty in everything they do. They also have this diligence and a complete and utter commitment to one another. There is no question that they would ever be disloyal to each other. I think that's such a lovely quality.”

'Fungus the Bogeyman' begins at 6pm on Sunday on Sky 1