He meant it, too. A shadow passed over that open, honest face. He was troubled, and a little menacing. Whatever could have provoked this dark reaction in such a famously affable fellow?
To understand that, you need to know that he had spent the morning pretending to be a paedophile. Whately will be the male lead in Paula Vogel's Pulitzer prize-winning play, How I Learned to Drive, when it opens in London on Wednesday. He will be Uncle Peck, a traumatised war veteran who goes to great lengths over many years to cultivate the closest of friendships with his niece, Li'l Bit.
As we sat discussing the play in a restaurant near the rehearsal studios, I listened out for the whispers at neighbouring tables. But nobody said, "Isn't that Thingy from Inspector Morse?" Nobody muttered "Lewis!" under their breath in imitation of John Thaw's distinctive bark. Neither did anyone seem to recognise the star of Peak Practice, the medical drama that made Whately a proper heart-throb, the Boy Next Door from whom many viewers would like to borrow more than a cup of sugar.
Perhaps our fellow diners could not hear that distinctive Geordie voice, with its matey rhythms and slight whine. Or perhaps the lack of recognition was because he looked rather less than a sex symbol in the flesh, with enough bags under his eyes to take a family on holiday. His face still had a weary charm, but the student-length hair was thin and straggly. At 47, he is older than you might think.
Whately was friendliness itself when our conversation began, sipping from a pint of lager between thoughtful answers. Why had he chosen to do this play, now? "When you get to the end of a TV series, you feel totally out of sorts as an actor. You feel unfit, your voice box has collapsed on you because you've spent all day muttering into a microphone that's two inches from your head, and you feel desperate to spread your wings and do a bit of real thesping."
It was television that made his name, of course. After a false start in accountancy, the shy young man from north Tyneside attracted attention as Neville in Auf Wiedersehen, Pet. He played Lewis for 12 years before calling time on Morse's sidekick. Despite a cameo role in The English Patient, he has not had a film offer in more than two years. In contrast, the collegiate approach to subsidised theatre is still attractive to a man who remains uneasy with his fame and wealth. "In TV, you just have to decide the night before exactly how you're going to say it and stick with that. You can't kick it around, you haven't got time. The idea of doing some rehearsals felt like a holiday, and is."
But why this particular play, a challenging and unconventional drama that enlists the chorus from Greek epic theatre in its exploration of a highly sensitive subject? "I thought it was extraordinary; not straightforward and linear. I could tell it would be exciting to work on."
Thanks, in part, to the film Lolita, the subject of paedophilia has been the subject of vigorous debate for some months. "That was a worry. But this is a different kettle of fish from Lolita, because it's told from the woman's point of view, and the overriding emotion in it is forgiveness. It is a fantastically warm piece. There's so much hysteria about paedophilia that nobody seems to be pausing for thought. If I was a paedophile, I would be going underground very fast. To save kids in the future, we need to air it and talk about it and treat it and discover exactly where it is coming from."
Uncle Peck is not a rapist - his desire is to be wooed by Li'l Bit rather than to attack her. But could this character engage an audience's sympathy? "I know he's sympathetic. He's a southern gent who's been damaged. There is a recognised syndrome in the States of war veterans whose trauma can result in this paedophiliac disposition. In the play, it's hinted that he was abused as a child himself.
"He's crafty in that he makes sure the child takes all the steps towards him. He stands back with arms open. But the warmth in the play comes from her recognition - in hindsight - that he empowered her to get away from a horrendous family background. He teaches her to drive, and he has faith in her, even if it is part of trying to gain her trust in order eventually to take advantage. He's waiting throughout the play until she's 18 to consummate what has become a love affair."
The strength of the casting is such that we do not expect that nice Kevin Whately will be the villain. And yet he has supplemented his lucrative roles as Lewis and Dr Jack Kerruish with a surprising number of bad guys on the stage and screen, most notably a wife-beater in the BBC's dark thriller, Trip Trap. Even then, many viewers had to fight the urge to forgive him.
"I don't like two-dimensional characters who are obviously villains from the moment they walk on stage. I don't believe for a second that any of us would recognise a paedophile if one walked in. If we can't see the side that Li'l Bit warms to and trusts so implicitly, way beyond the rest of her family, then you've lost the battle. You're not telling the story."
Which is all very commendable, but there was one more big question to ask about this part - and it was the one that threw him. Whately is the father of two young teenagers, Kieran and Catherine. What would he do if a paedophile like Uncle Peck got his hands on one of them?
"It hasn't ... er, it hasn't crossed my mind in such a bald way." There was a pause. "Yeah, I mean ... that's why it's such an emotive subject. It's very easy to stand back and say, 'Oh these people are sick and they need treatment.' But if my daughter was being abused? I dare say I'd take an axe to someone."
When the script came in, he discussed it at length with his wife Madelaine. "She was asking, 'Why do you want to do it? Would you let the kids see it? If not, why do it?' I said I wouldn't let the kids see it, but having started it, because they're teenagers now, if they were interested and wanted to, I would let them. I suspect my daughter will see it."
Why had he been so reluctant initially? "Purely my own embarrassment at her seeing me groping a young girl. But she's a very together person and - what did I just say? I've never said anything like that in my life. 'She's a very together person?' Don't print that! No, she's a very bright, mature girl, and she'll understand it."
! 'How I Learned to Drive': Donmar Warehouse, WC2 (0171 369 1732), previewing now, opens Wed to 8 Aug.Reuse content