There's not much of John Simm's work that his young son can watch. Paul Abbott's political thriller State of Play, in which the Leeds-born actor played a crusading journalist? Too narratively tricksy, and there's swearing. Life on Mars? Dad gets shot, then disappears back in time.
Sex Traffic? Gruelling and graphic subject matter. English Civil War drama The Devil's Whore? The title alone was a no-no. This year's ageing-lads-on-hols Mad Dogs? Yes, it was sunny, and Dad was playing with his old Life on Mars mucker Philip Glenister, but they do help dispose of a bloody corpse...
Last year's sold-out run of Hamlet at Sheffield's Crucible theatre? Shakespeare's a bit much for a nine-year-old, even if his dad is one of the most watchable actors in the UK, whether on stage, small screen or big screen.
"It is always," Simm notes wryly but not unhappily, "very heavy."
Praise be then for Easter 2009's rare family treat, Skellig on Sky1, in which Simm played a harried dad who can't get his head round the fact that his son's found an angel in a shed at the bottom of the garden. And thanks, too, to a certain Gallifreyan Time Lord.
"That's why I did Doctor Who," admits the 40-year-old. "To prove to my son that I wasn't lying. 'I am actually an actor. Honestly - that's the reason I go to work and don't come back for months…'" Simm laughs.
We'll set aside the fact that, in his most recent appearance as the Master, nemesis of the good Doctor, Dad tried to polish off David Tennant. And, rather creepily, he appeared on screen in multiple simultaneous incarnations, some of them wearing ladies' clothes.
The role served to prove how he spends his long absences from the family home in north London he shares with his wife, actress Kate Magowan, and two children (son Ryan and Molly, four); and it gave his son peerless bragging rights in the playground.
Alas, with his new drama, Simm is again off-limits to his children. In Exile he takes drugs, slaps his ex, tries to drown his own dad and gets argy-bargy in the face of not one but two venerable old gentlemen of British thespianism, Jim Broadbent and Timothy West.
Based on an original idea by Abbott and written/developed by Danny Brocklehurst (Clocking Off, The Street), Exile is about a not-so-prodigal son - a once-successful, muckraking celebrity hack (Simm) returning in disgrace from London to his childhood home in Lancashire.
In his prime, his father (Broadbent) was a campaigning local journalist. But now the old man is imprisoned in his own mind, suffering from Alzheimer's. His condition alone would be trying enough to deal with. But the son also needs to confront his father over the savage beating he meted out to the lad 17 years previously after finding him snooping in secret files in his office.
Simm concedes that he almost didn't even read the Exile script. He'd been away from home for an extended period doing Hamlet and was desperate to spend some time with his family. But his agent persisted, telling him, "You've got to read this…" He did, and "It was too good to say no to. And also, after Doctor Who and Life on Mars, I wanted to get back to the stuff that I used to do - quite gritty realism. And this is it."
Exile is a thriller, but it's also a knotty family drama - a close-quarters look at fathers, sons, and the ties that bind. And the ties that twist. Simm, a voracious bookworm, says he has read the vivid and candid memoir And When Did You Last See Your Father?, by Blake Morrison.
But he didn't particularly draw on it - partly because the film adaptation starred Broadbent (who took the role in Exile after the late Pete Postlethwaite became too ill to appear), "and that would probably confuse me a bit".
Also, Simm had his own experiences to reference. "I argued with my dad when I first left home, as all teenagers do," he says as he fingers a plastic cup at BBC HQ in west London. "But nothing out of the ordinary."
Indeed, his relationship in his youth with his dad Ronald seems pretty functional. Almost groovily so - they gigged in a band together in working-men's clubs. "But there were little parallels [in the script]. I left home when I was 17, I came down here. And to have to travel back and see your old school friends, and you've had a bit of success - it's all a bit weird.
"I did that drive up north quite a lot, going back to that little town [he grew up in Lancashire] and dealing with that after being away so long, and living on a different planet more or less."
As a father himself, he's been chuffed to find something uniting three generations of Simms: Laurel and Hardy, a boxed set of whose films he and Ryan are working their way through.
"My dad would go red in the face and fall off his chair, crying with laughter at Laurel and Hardy," he smiles. "I laugh at it, too - not like that, I don't laugh like that in general! And my son laughs at it. That's unbelievable - three generations, and how old are those films? It's like it's from a time capsule. It's mad. I'm so, so glad that my son likes Laurel and Hardy."
As sons must do to their fathers, though, Ryan has visited one disappointment on Simm: "He won't watch them in black and white. It's the colourised ones for him, which is hard for me," he winces. "But at least he's watching them. His generation don't get things that aren't in colour."
His steadying paternal hand has failed him elsewhere, too. In his often lengthy absences on TV and film sets, his son is running riot, televisually speaking. "He watches those bloody reality shows with his mum, which I'm not happy about. The ballroom thing and the pop star talent s**t things. Which," he sighs, "I'm a bit p****d off about.
“But," he concludes with a what-can-you-do? shrug, "I'm not there though." Sometimes, despite a dad's best efforts, the apple does fall from the tree.