Rarely is there an actor more removed from his onscreen persona than Peter Mullan.

Genial and welcoming in person, the Peterhead-born actor has frequently been utterly chilling in his 25-year screen career, from the emotional breakdown he played in Tyrannosaur to the husband who sells his wife in The Claim. When the Harry Potter team needed an actor to play that brutal Death Eater Yaxley, they turned straight to Mullan.

He is, of course, far more diverse than simply a rent-a-madman – as shown by his Cannes Best Actor prize for his recovering alcoholic in My Name Is Joe. But there's something quite delicious about 53-year-old Mullan at his most menacing, as his new six-part TV drama Top of the Lake shows.

"He's a baby. He's a baby," Mullan chides, referring to his character, Matt Mitcham, but in truth there's little innocent about this father-of-three. Murder and drug-dealing are all par for the course.

Top of the Lake relocated Mullan for several months to New Zealand's South Island, just outside Queenstown. He immediately felt welcome: "I really like Kiwis – a great attitude. The Kiwi sense of humour is very similar to the Scots – dark and self-deprecating, and if somebody is behaving like a p***k, they'll tell you you're behaving like a p***k. And I like that. Very straight."

You can easily say the same about Mullan. His character in this drama – created, co-written and directed by Kiwi filmmaker Jane Campion – is a tightly coiled presence who strikes fear into the community. The story begins as Mitcham's half-Thai 12 year-old daughter Tui (Jacqueline Joe) walks into the local lake as if to kill herself, then disappears. Unbeknown to anyone, she's pregnant. "It's quite Twin Peaksy," says Mullan. "Who impregnated this little girl?"

He knows only too well the fear a parent can strike into you. His own father, a toolmaker who would "suck the life out" of any room he entered, spent his adult life in a drunken stupor. "Some countries shouldn't drink alcohol – including my own," he says wryly. Domestic violence was a regular occurrence, and he ploughed much of this experience into the booze-addled patriarch he played in Neds, his recent directorial effort.

Co-starring Holly Hunter and Mad Men's Elizabeth Moss, Top of the Lake may have jolted some memories, but Mullan seems delighted to be involved: "I don't think of it as television. I think of it as a six-hour-long film."

When we meet, it's at the Berlin Film Festival, where all six episodes were screened – symptomatic of how television is enjoying a golden age. "The ground has moved so much and the boundaries have blurred so much - every day to me felt like doing a movie."

Curiously, Mullan has been noticing this shift towards television in another way. He's currently looking for financing for his fourth film as director, a story about Hurricane Katrina that will cost in the region of $15-$20 million.

"You cannot get that money in film. You just can't."

The BBC even asked if he'd consider turning it into a multi-part drama. "They said 'Can you do it as a series?' and I said, 'No, it's a movie. It's an hour-and-a-half long. There you go, that's it.'"

Dressed in jeans, a black jacket and white dress shirt, and sporting a goatee, Mullan is all too aware that budgets for the sort of independent films that are his bread-and-butter are diminishing. "It's been a really tough couple of years," he says. "I've been lucky because I get to work abroad and stuff."

Indeed, from being a "spear-carrier" in Braveheart to an amiable drunk in Steven Spielberg's War Horse, Mullan has maintained an international profile – enough to help support his four children, at least.

He's recently completed work on Dexter Fletcher's Sunshine on Leith, a Mamma Mia!-style musical about two lads returning from Afghanistan that's set to songs by The Proclaimers. "It's very light. It's not a heavy piece at all," says Mullan, who even gets to sing. "I redefine singing," he jokes.

"Imagine what you mean by singing and stretch it as far as you can go." So there's no chance of Mullan recording an album in the near future? "Only if I wanted to inflict enormous amounts of pain."

He is as delightfully blunt as ever, particularly when it comes to why he still acts. "Acting gives you an income, gives you money. I'd starve to death if I was just writing and directing – it doesn't pay. You try to raise the money for a couple of years - by the time you get paid you're already out of pocket for the two years you've not been earning any money. So directing doesn't pay, whereas acting does, and it's more fun. Directing, though, is more gratifying."

In particular The Magdalene Sisters which, 11 years after winning the Golden Lion best film award at the Venice Film Festival, is still making waves. After a 10-year campaign, stirred up by his film, as well as sundry stage plays and a documentary by Steven O'Riordan, the Irish government finally apologised earlier this year to the 10,000 women who were locked away in Catholic workhouses and subjected to brutal childhoods.

"I was delighted that they finally got the apology," Mullan says, cracking a smile. "Somehow, it's moments like this that make the independent film struggle worth it."

Top of the Lake, BBC Two, Saturday, July 13, at 9.10pm.