If this were anyone other than David Morrissey, such ordinariness would go unremarked. But the Liverpudlian actor has so specialised in roles that peel away nondescript behaviour to reveal utter derangement, it's hard to take him quite at face value. You keep expecting the smile to freeze, the eyes to narrow to a squint, and something rather unpleasant to happen. When it doesn't, it's almost a blow, particularly after watching Big Cat, a one-off drama by Lucy Gannon (the prolific power behind such high-ratings series as Soldier, Soldier, Peak Practice and Bramwell) which is being screened tomorrow evening on BBC 1.
Morrissey plays the lead, an energetic man called Leo who is dubbed "big cat" by Alice (Amanda Root), the lonely thirtysomething he woos with a noli me tangere restraint that at first seems comically old-fashioned and then creepily psychotic. He delivers an intense performance that somehow manages to retain our sympathy for a character who engages in compulsive DIY, cleaning and treating his woman like a doormat in order to preserve the fantasy America he has inhabited since he was a child, sheltering from an abusive home life.
Leo could be described as the apotheosis of a part the actor has been making his own during the Nineties: the man who is "not quite all there". Last year, his portrayal of Bradley Headstone, forever lurking in the shadows of Julian Ferino's crepuscular BBC dramatisation of Dickens' Our Mutual Friend, made for compulsive viewing: initially the epitome of stern- eyed, taciturn rectitude, by the end his schoolmaster was a haunted, sobbing wreck.
Before that, he cropped up as Shaun Southern, a tax inspector accelerating towards crisis in Tony Marchant's chronicle of chaotically related London lives, Holding On (again for the BBC). Southern's obsession with trying to track down fraudsters visibly started to splinter under the weight of personal guilt.
Looking at the 34-year-old's television CV, it's hard to spot a character that wasn't subject to a similar mental upheaval. In the gritty Sheffield- set police drama, Out of the Blue, he showed a good cop, DS Lewin, cracking up under the strain of work; in Lynda La Plante's Framed, he was again the honest cop who lets it all go, this time seduced into a life of crime by a rich supergrass. In his next project, the film for which he has been growing a beard, Fanny and Elvis (to star Ray Winstone and Kerry Fox), he plays a psychology lecturer in a northern college - whose marriage is, guess what, falling apart.
Part of the reason he continually gets to play these obsessives is, he believes, to do with the cautiousness of the television industry. "The turning point for me was a Central film made in 1989 called The Widow Maker, in which I played a man who goes berserk in a small Midlands town and shoots 10 people. After that, I got offered a lot of heavy stuff. Because drama series operate on a slow burn, the programme makers want to let the audience know in advance what they're going to be watching, so they tend to want actors to take on similar roles from one series to another."
Not that he's complaining about the niche he's found. He relishes building each character anew, both through assiduous reading and inner burrowing, and savours the complexities these kinds of parts afford. "I don't approach them as deranged people, or villains. In fact, I try and imagine what their ordinary day-to-day lives would be like, because they perceive themselves to be normal, and the world around them as mad. I don't think that is exceptional. You can see people like Leo all around you. They might not end up violent towards others but they might do great harm to themselves."
He denies being any more temperamentally suited to these angsty souls than anyone else: "I tend to play characters who have an edge of depression about them. They are on the outside looking in. There is a side of me that has that, but the same is true of everyone. If I do have obsessive tendencies, playing these roles tends to exorcise them. I never take things home with me apart from my hair dye."
Home is his partner, the novelist Esther Freud, whom he met seven years ago, and their two small children; a world off-limits in interview.
Growing up on a council estate in Knotty Ash, Liverpool - the youngest of four children, his father a shoe-repairer, his mother an employee of Littlewoods - he was fascinated by TV and film, particularly musicals ("Gene Kelly was the person I wanted to be").
He got involved in youth theatre at the Liverpool Everyman and got his first break at the age of 17 after leaving school, with no qualifications, in One Summer, a Willy Russell five-parter for Channel 4, about two Scouse lads who have the holiday of their lives in Wales. That confirmed his vocation in his family's eyes (although his father had died two years previously). After travelling, he took a place at RADA.
Morrissey these days is unknown as a stage actor, but during the Eighties, he was in the ascendant, most notably playing Peer Gynt at the National and the Bastard in Deborah Warner's King John at Stratford, as well as stints with Manchester Royal Exchange and Cheek by Jowl. But he grew disillusioned and stopped accepting roles: "I did four years of solid work and remember getting a letter from my bank manager telling me I was overdrawn. It wasn't as creatively or financially rewarding as I wanted it to be."
When I suggest that Morrissey's talent might be more widely recognised if he had stuck with theatre (many the films he has had bit parts in - Waterland, Being Human - have sunk away quietly), he shakes his head: "I don't feel underrated. I get lots of jobs. I suppose I'd like to have my work seen on a bigger scale, but only because the more successful you are, the more choice you have in getting challenging roles."
A glance at his future schedules suggests that that time may be drawing close. Later this year, he stars in Hilary and Jackie, based on the controversial biography of Jacqueline du Pre, in which he plays the part of Hilary's husband, Kiffer, the conductor who had a sexual relationship with Jacqueline (played by Emily Watson) when the latter was having a nervous breakdown.
For once, Morrissey couldn't have landed a sounder character: "He doesn't have a secret agenda or a ticking timebomb. He's a genuinely good man."
He sounds genuinely pleased. If the film finally communicates David Morrissey's considerable talent, and grounded personality, it might be his most cunning move to date.
Big Cat is at 9.20pm, Sun, BBC 1