The nicest grump in Britain is Michael Palin

Michael Palin spent his 75th birthday in North Korea filming his latest documentary. Photo / ITN Productions

Michael Palin's 75th birthday celebrations might not have suited your average pensioner.

No party for the ever-youthful, globetrotter. Instead, he packed a case and headed for North Korea.

On the day itself, last May, you would have found Palin tilling soil alongside a peasant woman in a workers' collective - all part of his latest documentary for Britain's Channel 5 which airs next week.

"When we finished, the director asked if she'd give me a job and, without pussy-footing around, she said, 'No, he was completely useless'!" laughs Palin. "It was refreshing because, out there, most people know nothing about documentaries and couldn't care less. My value to her was zero."

It's a different story at home, of course. To us, Michael Palin CBE, is the most esteemed of polymaths - comedian, writer, actor, presenter. He's a bona fide national treasure who's been delighting us for five decades.

Do people behave peculiarly around him?

"I don't think so" he says, "because, hopefully, I'm just the me I've always been. I've been married to the same woman for 52 years, and we've lived for 50 of them in the same north London street. I travel to work on the Tube and if I'm bothered by anyone - which is rare - it's always in a genial way."

The only thing that's off limits, he adds, is "a quiet beer in the corner of a pub". "People who've had a few drinks will suddenly become rather loud and want you to do Monty Python sketches. But, otherwise, I just carry on. I'd never want to be a prisoner of my own fame."

Accordingly, Palin has arrived at the Covent Garden Hotel, today, under his own steam. He is full of bonhomie. How disappointing if - despite the Nicest Man in Britain label that makes him groan when I mention it - he had turned out to be grumpy.

"I'm as grumpy as the next man. It drives my family crazy that I'm always referred to in glowing terms," he smiles. "I think it started as a kind of joke and stuck."

If he wants to shake the reputation off, he might call his old friend John Cleese, who's currently courting opprobrium with his decision to leave Britain and flounce off to the Caribbean.

"You have to remember that what keeps John healthy and engaged with life is a restlessness and a general level of complaint about this, that and the other," says Palin. "The struggle for a perfect life will keep him going for a very long time.

"Also, he has some form," he adds, laughing. "He's been to the Caribbean for good before and I dare say he'll be back. I certainly hope so."

Despite the ribbing, and their many differences - Cleese, for example, is on his fourth marriage, while Palin has been with Helen since the age of 16 - they're clearly close.

"John still makes me laugh," says Palin. "We're interested in each other's lives, although if I mention my travel shows, John will do one of those big, stifled, stage yawns. It's a standing joke between us."

Palin groans again, when I mention Shane Allen, the former BBC head of comedy who recently declared that, in the name of diversity, the corporation would never commission Monty Python (featuring six Oxbridge-educated white blokes) today.

"Yes, the world has changed and there may well be a lot of people writing comedy who are, say, from a black minority, who are not getting a chance. And they should be," says Palin. "But it's barking mad to single out a group like Python and say you wouldn't commission it because, manifestly, Python has continued to be popular.

"I'm all for diversity, but shouldn't that mean everyone - including Oxbridge-educated white men, who happen to be funny? To shut the door on anyone seems utterly crazy."

Just as well Palin has so much else up his sleeve. He's currently starring in ITV's adaptation of Thackeray's Vanity Fair, and is publishing a new book, Erebus, an account of one of the great 19th century exploring ships.

Then, of course, there's the North Korea documentary. With perfect timing, Palin and the crew landed in Pyongyang just days after surprise talks between the North and South Korea leaders, Kim Jong Un and President Moon Jae In.

Although policed by government minders, the team was able to travel extensively, capturing the weird and sometimes wonderful aspects of a country that Palin says was "completely different to anything I'd ever encountered".

"There was electronic music piped into the city at 5am; pastel-painted skyscrapers; the complete absence of pollution, internet or advertising," he muses. "There was a kind of innocence about a nation where the leaders are seen as fathers, protecting their people by keeping their minds as pure as the skies above."

Despite that, he continues, "They worry about how they look, how they bring up their children and what they eat. There's more that unites us than divides us".

Who better than Palin, who wears his geniality as others wear a flak jacket, to penetrate the basic humanity of North Koreans? Where others might have brandished microphones and demands, he ingratiated himself by showing pictures of his grandchildren.

He has four, by the way, from two sons and a daughter. "Everything they say about being a grandparent is true," he says. "It just seems to melt you a little bit."

It's the cherry on the cake of his relationship with Helen, a former teacher, who has been with him, he says, through the good times and bad.

"Maybe our marriage has lasted so long because Helen didn't marry a celebrity. She married someone with a shared sense of humour, who mucked about and didn't have much of a job at the time," he explains. "What we liked about each other then we still like now. I can't imagine life without her."

The bad times include his elder sister Angela's suicide in 1987.

"You don't just get over someone's suicide; it reverberates throughout your life," says Palin. "I still miss her and am happy to talk about her because, otherwise, I'd be treating her like a victim or someone defined by her death - whereas, for me, she's defined by her life. She was a brilliant person who became depressed and in the end felt she was a burden, which is so weird because we valued her so much. When I think of her, it's the wonderful things I remember."

Same goes for his old Python pal, Terry Jones, whom he has known since they were at Oxford. He is now stricken with a form of Alzheimer's that has robbed him of his ability to communicate.

"It's particularly cruel, because words, humour and self-expression defined him," he says.

Palin takes Jones to the local pub. "There are moments with him that are still so valuable. He will squeeze my hand or laugh at something I say, or a recollection of someone we both knew. And although, in the end, the prognosis is that even this will go, I would never want to stop seeing Terry because I'm just so fond of him."

Hardly likely, then, that Palin is going to lose The Nicest Man in Britain tag any time soon.