Saints alive! Is that my car? Sir Roger Moore is the special guest on a show that restores classic cars like The Saint's Volvo - and it brought the memories flooding back 

This is all wrong. It's like hearing that Joan Collins shops in Lidor that Russell Brand plays golf. It's just a showbiz impossibility. Yet Sir Roger Moore insists it is true. These days he drives not a Rolls-Royce or an Aston Martin, as one might expect, but a Smart car.

Yes, the one-time James Bond, and still one of our most dapper knights of the realm, is often to be found unfurling his elegant frame from a car that even he describes as a 'tin can'. 

'Well, if you live in Monaco as I do,' he says with his trademark languid delivery, 'you know that parking is an issue. It's much easier to park a Smart car than a Mercedes.'

Roger Moore's latest TV appearance will make car addicts swoon. He's the special guest in an episode of Car SOS, a TV show that sees neglected classic cars brought back to their former glory. The car in question in this episode is a Volvo P1800, the type Sir Roger drove on The Saint back in the 60s, above

Don't the good people of Monaco find it surprising to see Sir Roger exiting a vehicle the size of a shoe box? Of course they do - and this tickles him no end. 

'The other day I was getting into it outside the Hotel de Paris where I'd been for lunch. The friend I was with told me that someone was sitting outside at a table and said, in a cockney accent, “What's James Bond doing getting into a tin of Heinz Baked Beans?”'

He has, as you would expect, driven some very James Bond type cars over the years. 'I've trashed a few in my time too,' he says, mischievously. 'It plays havoc with the insurance.' He did once own a Rolls. Of course he did. 

Car SOS, which sees (left to right) Kelly Montague, Bobby Dallman, Fuzz Townshed, Tim Shaw and Michael Dallman hunting down charismatic cars with deserving owners and getting their motors back on the road, has been one of National Geographic Channel's most popular shows recently

'I'll always remember when I was convinced that it was finally within my price range. I was somewhat reluctant but it was delivered to Pinewood Studios three days before Christmas. I was going home to Devon and I remember thinking how thrilled my youngest son, who was three, would be if I drove home in it, dressed as Father Christmas. So I did.' 

I remember sitting at traffic lights in this car, dressed as Santa, and feeling the eyes of the person in the next car looking at me.' It wasn't, it transpires, a nice feeling. 'It was too obviously being flash, wasn't it? Showing off.'

We're talking cars because Roger's latest TV appearance will make car addicts swoon. He's the special guest in an episode of Car SOS, a TV show that sees neglected classic cars brought back to their former glory. The car in question in this episode is a Volvo P1800, the type Sir Roger drove on The Saint back in the 60s. 

Tim Shaw and Roger Moore at the Oakley Court Hotel during the episode, above

In its heyday it was one of the most lusted-after sports cars in Britain. Presenter Tim Shaw doesn't let the fact that this wasn't the actual car used in The Saint stand in the way of an endorsement from Moore. Tim is filmed trying to track down the star and he eventually meets a bemused Sir Roger, who agrees to sign one of the iconic red leather seats.

'It was a joy to find one of these cars,' says Sir Roger. 'This one had become a rusty shell. It was on blocks in a garage so it was wonderful to see it brought back to life. It's moving to see people's reactions.' What does he recall of driving the Volvo? Well, he remembers having to crash it into a tree once. Apart from that, he mostly remembers what a nightmare it was to get in and out of. 'Low, you see,' he points out.

Car SOS, which sees Tim and his co-presenter Fuzz Townshed hunting down charismatic cars with deserving owners and getting their motors back on the road, has been one of National Geographic Channel's most popular shows recently. This is the fourth series, and in the past they've done up everything from E-Type Jags to Alfa Romeos - they even brought an Austin Healey Sprite that Stirling Moss raced in 1962 back to life before putting Stirling back in the driver's seat.

The story of what happened to the Volvo is actually a very touching one. It had been bought by a car enthusiast (and Saint fan) who planned to restore it himself, but suffered a stroke and wasn't able to see the project through. Tim and Fuzz take over where he left off, however, stripping the vehicle down and turning it from a rust-mobile into a sleek sports car once again.

It has to be said that Sir Roger, 88, has aged better than his car. He has been through his very own refurbishment though. In 1993 he had prostate cancer and then in 2013 he was diagnosed with Type 2 diabetes which has led to a lifestyle overhaul. Gone are the Martini cocktails, ditto his favourite Sancerre. Today he sips only Diet Coke.

He admits that his fast and furious days are long gone. Another casualty has been his annual ski holiday. 'I used to think my life was skiing. I couldn't think of anything better to do than ski, ski, ski. But when the knees go you can't ski any more. Or play tennis.'

Even his yacht has gone. 'The boat's gone now because my knees gave me such trouble I couldn't get in or out of it. Even if I could, I'm not supposed to go out in the sunshine. We all used to think the sun was so good for us and now we learn it's bad. I've spent my life having bits cut off me because of skin problems. When they put me in the box, if they want all of me they're going to have to go around all the pathology labs in the world to find the rest of me.' As is his wont, he turns any notion of alarm into a joke. 'I'm not planning on going, by the way. I feel fine.'

'It was a joy to find one of these cars,' says Sir Roger. 'This one had become a rusty shell. It was on blocks in a garage so it was wonderful to see it brought back to life.' Above, the Volvo P1800 at the Car SOS Workshop

One imagines a Smart car might not be best for his knees, but he's almost evangelical about his little runaround. Not least because it means he can drive himself - and his wife - around. Again, one imagines that Sir Roger Moore wouldn't be short of a chauffeur. 'Oh, I hate being driven. I like to drive myself, always have. Now I just drive my wife though. She doesn't drive. Thank God she doesn't. She relies on me. I drop her off and she goes shopping and then I pick her up again.'

His wife, Kiki Tholstrup, is his fourth. They married in 2002 and he cites her as his 'rock'. His previous wives sound quite a handful. The first was ice-skater Doorn van Steyn, who threw alhis clothes in a bath of hot water when they rowed. His second, Dorothy Squires, smashed a guitar over his head and his third wife (the mother of his three children), Luisa Mattioli, used to demand to be on set at his James Bond love scenes (according to Roger, she'd say, 'I know it's your job, just don't enjoy it').

And now he has Kiki, who also loved skiing but has given it up out of love for him. It's also Kiki who encouraged him to change his diet. 'What is the secret of my good health? It's a good wife,' he says.

He's in fine fettle. His hearing might not be what it once was (he apologises for being slow on the uptake) but his sense of humour is intact, as is his man-about-town style. Today he's dressed in (what else?) a blazer and slacks.

He's still sending himself up relentlessly. It's become a habit, he acknowledges. It started when he thought he should do it first, before others did. 'I always make a joke of everything. If I hear myself on radio or see myself on screen, I have to laugh. I've made jokes myself about how I've only got three expressions. Years ago my agent said. “You must stop saying these things or people are going to believe them.” I said, “Well, I believe them.”'

Today he jokes about the difference between him as James Bond and Daniel Craig as Bond. 'Daniel's extraordinarily athletic; he looks as though he could kill somebody,' he says. Then he smiles. 'The most dangerous part of me was my lacquered hair.' His Bond wasn't as much of an Action Man either. 'When I saw Casino Royale I noted Daniel Craig did more action in the first 30 seconds than I did in 30 years. Extraordinary.'

He's surprisingly unshowy in the flesh, and he offers some surprising observations about ageing. While his cars are getting smaller, he says, his shoes are getting bigger. 'I've just found the most comfortable shoes of my life,' he reveals. 'They're by Armani and they look like sports shoes. Feet have suddenly become very important - not just things stuck at the end your legs. Mine seem to have continued to grow. Every pair of shoes I own seems too tight.'

And this from a man who, back in the 60s, once forked out 60,000 lira (equivalent to £630 today) on a pair of crocodile shoes. It's a pity he no longer has them, as they too would be a collector's item by now. 

Roger is on Car SOS on Thursday at 8pm on National Geographic Channel.