Momentarily I mistake him for a bike messenger – and it turns out that Hannah has indeed just got off his bike.
After their four-year-old twins, Gabriel and Astrid, were safely delivered to their Surrey school this morning by Hannah and his wife, Glasgow-born actress Joanna Roth, he set off on a two-hour bike ride.
For the good of his health, or sheer pleasure? "Oh, I've always been pretty fit," replies the doe-eyed one, flashing a whiter-than-white smile and pulling off his beanie to reveal a halo of greying curls.
Of course, a whole generation of women would agree that John Hannah, actor, has always been both pretty and fit. Indeed, a lot of gay men thought so, too, when he became an icon for them after his poignant reading of W H Auden's Funeral Blues in Four Weddings and a Funeral.
And it is a view that will remain unchallenged when the 46-year-old from East Kilbride reprises his role as the ne'er-do-well Jonathan Carnahan in the third of The Mummy series of Hollywood period horror blockbusters, Tomb of the Dragon Emperor, to be released later this summer.
Meanwhile, in Cannes this week, a much more modest film provides yet another showcase for Hannah's talents. Despite some dodgy facial hair, he gives a near-perfect performance in actor-turned-writer-director Bruce Robertson's lovely short film, Zip N Zoo, which Hannah made in Scotland.
At the French film festival, the feelgood Zip N Zoo is the jewel in the crown of the Highlands and Islands Film Commission's bid to sell the beauty of Scottish locations for international film-makers.
"I did Bruce's film because he sent me the script and I really liked it; it's different, such a sweet little film," says the hyperactive Hannah, devouring a salmon salad. "And making Zip N Zoo was a great opportunity to spend time in a stunning part of Scotland – Assynt in Sutherland; I'd never been there before.
"Oddly enough, I do actually like Scotland," he continues, referring to the fact that he's been on the receiving end of some flak in the past for speaking his mind about the state of the nation. He's particularly scathing of sectarianism, saying he never wants his children to grow up among such bigotry, even calling Scotland "a strange little wet, fried, angry place".
When an Italian journalist asked him what East Kilbride was like, he compared it to Milton Keynes – "and managed to p*** off people in both towns. Some going!"
"I don't know why people expect you to leave a place and then say wonderful things about it," he continues. "If it was so bloody wonderful, then you probably wouldn't have left in the first place. If I'm critical, it doesn't mean I hate everything about Scotland. I got jumped on, though, especially for what I said about East Kilbride, my hometown – where my folks still live in the same council house that I was born in, incidentally.
"But I do like going back to Scotland, despite the bad press I've had, although I can't imagine living there again – even somewhere as beautiful as the location for Zip N Zoo."
In the film, he plays Tom Gunn, a likeable village schoolmaster married to Marion (Simone Lahib), who is desperately trying to have a baby. Then Natalie, a 19-year-old from Brooklyn with impossibly blonde hair and a corn-fed complexion, turns up, announcing that she's Tom's daughter. She's played by Remy Bennett – granddaughter of the legendary crooner Tony – who has the face of an angel and the voice of a seductress. "A real find!" exclaims Hannah.
The scenery is gorgeous, the acting subtle, the story both funny and touching. The title comes from a phrase used in fly-fishing to describe the timing of the casting of an angler's fly. And the film also gives new meaning to the term fly- fishing, when it emerges that his daughter dates back to the days when, as a penniless student in the States, he became a sperm donor. It's this "employment" that gives the film its final twist.
In his poverty-stricken years as a resting actor, of which there were more than a few, was Hannah ever tempted to earn some cash on the side, so to speak? "No", he grins. "But, hey, I wish I'd thought of it."
Nonetheless, he's ecstatic about becoming a father – he took a year off work when the twins were born – and can't stop talking about them.
"Exhausting, though!" he says, slumping back in his chair. "But it's great being a dad. Joanna and I did lots before we had them and she helped me to deal with a lot of stuff, the adversities you go through in this business, as well as personal things. We travelled extensively and did loads of work, although her career went on hold for a couple of years, because having kids coincided with her getting to an age (42] when the parts for women are fewer.
"When she goes up to play a mother of two, say, well, I wouldn't cast her – not unless I was looking for a glamorous mum. Not that she goes around the house in high heels and wee short skirts doing the Hoovering. Well, maybe sometimes! She's done a couple of jobs recently, though.
"In fact, we had wee holiday booked in Devon recently and she got a job, so I went on my own with the children. I'll never do it again. It was so hard! They were mean to me. I was suicidal by the end of the week. They just wouldn't do anything for me – eat, sleep, get dressed. I couldn't get them out of their jammies until three in the afternoon. I tried everything, holding bits of chocolate over them …
"Who do they take after? Genghis Khan and Attila the Hun! Seriously, they are just very like themselves, both very different."
Having children is all-consuming, he says, adding that in his younger days he battled with depression, but having the twins has left no time for dark moods. "I'm an 'up' kind of person anyway. Of course I get down, but much less so since they came along."
After leaving school at 16, with six O-Levels, he trained as an electrician and worked on a stall at the Barras, in Glasgow. He drank far too much in his younger days and continued doing so after training as an actor at the Royal Scottish Academy of Music and Drama in Glasgow. It was ten years before "overnight stardom" came along with Four Weddings and a Funeral , then Sliding Doors with Gwyneth Paltrow.
Nowadays, though, rather than getting wellied he prefers playing a round of golf, going snowboarding or cycling, or reading a book. Surely not a Rebus novel? He filmed two of the books and was much criticised for being too young and pretty to play Ian Rankin's grumpy old cop.
"It was never my idea to play him myself," he says. "My company, Clerkenwell Films, made the first two and the only way we could get the commission was if I played Rebus, who was actually the same age as me at the time, 37. So I felt that gave us the licence, but I took a bit of a kicking. I never wanted to make all eight, anyway. And Ken Stott's brilliant – I always wanted either him or Peter Mullan to do it. You know, I don't watch television. The BBC really messed up the legal drama series, New Street Law, that I was in. The women in it were such weak characters – and this was a show made by three strong women – they were like girls on the make-up counter at Boots. No offence to shop girls, but these women were meant to be smart lawyers."
Unbelievably, for an actor who can command more than a million dollars for his role in The Mummy , Hannah still has fallow periods. "I'm in one right now," he sighs heavily.
"Looking for work as an actor in this country is like going fishing," he adds, clearly still smarting from the fact that he's been turned down for Ivanov, at London's Donmar theatre, opposite Kenneth Branagh. "Already this year I've lost two jobs," he says, spearing a green bean. "First, I didn't get Ivanov, then I went up for Adrian Shergold's new TV film, which he's making in Scotland with Gina McKee, and I didn't get that either. I really wanted that job.
"To be honest, I haven't read one script I like – all the TV I get sent is f****** rubbish. Pathetic! There's a big thing going up to Scotland, being made by Shed who made Footballers' Wives. It's a cross between Widows and Two Thousand Acres of Sky, with couthy Scots and Cockney gangsters' wives. We've had Whisky Galore, can we not move on and do something intelligent? I'll bet Michelle Collins is in it.
"So, no TV for me since I didn't get Adrian's gig. Dammit! I might go to Oregon in July to make a little film, but it depends on dates. The Mummy opens in China and then I want to do a big tour of the Far East with the family."
Lately, though, he's been spending time moving house. He and Roth – whom he met and pursued passionately when they were both playing in Measure for Measure at the National Theatre – moved from their home in Richmond, West London, to Oxfordshire. They lasted less than a year and have just moved back. "So I've given Gordon Brown two lots of stamp duty," he moans.
They couldn't thole the countryside, he says: "Yeah, big house, big garden, sitting on my lawnmower watching the clouds go by. It was horrible! I hated it, so did Joanna – and she's the boss."
• The Screen Machine tours Zip N Zoo around the Highlands and Islands in the autumn.
• The Mummy: Tomb of the Dragon Emperor is due for release on 1 August.