On November 20, 1944, a US P-47 Thunderbolt nicknamed Peggy III was hit by flak while returning from a dive-bombing mission over the German city of Bonn. Its 25-year-old pilot, Captain Robert J Bradford, was killed attempting to escape his burning aircraft, which subsequently crashed near the village of Liblar. The young US Eighth Air Force pilot, a member of the 56th Fighter Group, 63rd Fighter Squadron, had grown up in Dallam County, Texas, and trained as an architect before learning to fly and travelling halfway across the world to fight the Nazis.

Fellow airman Randel L Murphy Jr recalled: “The last time I saw him was at approximately 11:20 hours and it looked as though he had broken for the deck from which there was a lot of light flak and 40mm. I called him and there was no reply.” Aside from the obvious family tragedy represented by Bradford’s loss, you might wonder about the relevance. After all, some 26,000 members of the Mighty Eighth were killed in the European campaign during the Second World War.

But intriguingly, the Texan airman, whose remains were eventually interred at the Ardennes American Cemetery in Belgium, was the grandfather of British comedy legend and author Robert Newman. Having dated a young divorcee while posted to RAF Boxted outside Colchester in Essex, he left her pregnant, almost certainly without knowing it, when his aircraft fell from the sky in flames.

“It’s an incredible story,” Newman marvels today. “I’ve thought a lot about my grandfather over the years. A young man who came to Europe and never left…”

Neither does the remarkable tale end there. Newman’s mother was subsequently adopted and her own child, the comedian himself, was also put up for adoption after being born in Hackney, East London,in 1964. Out of respect for their family, he doesn’t name his mother or his grandmother.

“I never got to meet them but it was good to find out my mother had herself been adopted because she was a GI baby,” he says. “I don’t know if he [Bradford] even knew she was pregnant, but apparently it’s not that uncommon to repeat the pattern.”

At 61, Newman is now more than twice as old and then some than the grandfather he never met but the thread of history – social, military and family – runs through our conversation like the vapour trail from Bradford’s doomed Thunderbolt. Sitting in a north London cafe, the acclaimed stand-up comic, historian and author is a far cry from the floppy-haired pin-up of early 90s TV and radio. In his place, a thoughtful middle-aged man who stepped away from fame at the height of his success.

Just under half a century after Bradford’s aircraft went down, Newman and his then comedy partner David Baddiel took to the stage in front of 12,000 fans at the vast Wembley Arena in North London for the biggest comedy show ever at the time.

One of the night’s undoubted highlights came when the pair appeared as elderly professors presenting a serious discussion show – History Today – which soon descended into a torrent of childish, playground-style insults. The gloriously silly sketch had wormed its way into the national consciousness as a recurring part of their previous TV series – The Mary Whitehouse Experience – repeated ad nauseam in playgrounds across Britain.

It was, in many ways, a golden age for comedy, before the “dawn of the edgelords, where people wanted to show how close to the wind they could sail”. Even today, with someone of a certain age, you can utter the immortal catchphrase, “That’s you, that is” and they’ll know exactly what you mean.

Ironically, it would be Newman and Baddiel’s final show together even though their success opened the doors for a new generation of stand-up stars as comedy became the “new rock ’n’ roll” and ever-bigger venues, mega-tours and million-pound pay-days became the norm.

Today Newman, who lives with his wife, an environmental lawyer, and two children in North London, says that he got bored of fame, had a haircut and walked away. If he has any regrets, they’re not on display.

“We were offered another series [of Newman and Baddiel] by the BBC but I think we just felt tapped out,” he says. “The thing was, I didn’t love television. I didn’t think, ‘This is my home’. I used to get really bored in a make-up chair. When I was writing the sketch, I’d put in someone with a beard, then I’d have to sit there for three hours having one put on.”

Another favourite skit that presumably featured unwanted time in the make-up chair saw Newman as Robert Smith of The Cure, performing jolly songs like The Laughing Policeman in Smith’s distinctively sad voice. “I liked that,” he smiles. “After they did Friday I’m In Love, I just thought, ‘Robert Smith can’t carry a happy tune’, so I had him doing Roll Out The Barrel and the Hokey Cokey. When we eventually met, he wanted to know if we were fans, which we were.”

Does he miss any of it? “I could do with a tour bus now that I’m older, with a video player in it,” he smiles. “These days I’m strictly public transport, which I really enjoy, but every now and then you think it would be really good to have a tour manager ora tour bus.”

While he deliberately chose a less high-profile path than Baddiel and his other colleagues, Steve Punt and Hugh Dennis, he has never stopped working. “I still get a huge buzz from live performances, being on stage, doing a sound check, all those aspects of stand-up,” he says.

Touring his comedy, well-received radio series and documentaries, and a series of critically-acclaimed books, starting with Dependence Day in 1994, have kept him busy. Which brings us to the point of our meeting today – his brilliant new Second World War-set novel, Intelligence. It might be a coincidence that he’s named after his long-dead grandfather, but the story helped galvanise the new book.

It features two young Oxford philosophers, Texas-born Ida (a nod to his grandfather) and Merry, inspired in part by the real-life British philosophers Mary Midgley and Philippa Foot – among Newman’s real-life heroines – who are thrust into the world of intelligence gathering. The pair stumble upon secret German information that could change the course of the war – if only they can get someone to listen to them.

“It might have come from the feeling I sometimes have that no one’s ever listening to me,” he smiles. “But Ida and Merry are philosophers and women too, so nowonder they find people don’t want to listen to them.”

It’s a fabulously English kind of a novel, filled with understatement and dry wit and warm characters with plenty of stiff upper lip, and “Keep calm and carry on” about it. Newman hopes it’ll find an audience and, if there’s any justice in the world, a big and appreciative one awaits it.

“I didn’t go to Oxford and I didn’t study philosophy, but I got really interested in English philosophy between the wars because it’s ordinary philosophy, which I can understand because it does what it says on the tin,” he says.

“I was introduced to Mary Midgley, one of our leading philosophers, when she was in her nineties and still redoubtable. What I really liked about her was that she rebelled against the specialised language of philosophy and I could relate to that. The Oxford philosophers were also quite chipper and comic. I can’t abide that idea that, if you’re deep, you’ve got to be dark and miserable.”

Hertfordshire-raised Newman went to Cambridge having been turned down by nine other universities. “My teacher told me, ‘You’ll either get into Cambridge or nowhere’, and he was right,” he says. The early intelligence services were largely made up of characters from academia and society, although they “became more professional” as the war went on.

But many bonkers true stories were inspired by these incredible characters who suddenly found themselves in the thick of the fight against the Nazis, something he has faithfully reflected in his novel. “They were a good company when I was writing,” he says. “They allowed me to escape from the ugliness of this present moment we’re living in, into the relative tranquility of the Second World War!”

Newman’s wartime London feels real and vital, taking in Blitz-hit streets, the drab greyness of life and the notorious bombing of the Café de Paris in March 1941, which killed at least 34 people.

“They used to carry on playing when the bombs were falling because they were so deep underground they thought it was like Churchill’s bunker,” he says. Sadly, a bomb fell down a ventilation shaft and exploded above the dance floor.

In the book, Merry gets a job at the nascent Photographic Interpretation Unit, formed from the private company Aerofilms in Wembley, North London, before moving to RAF Medmenham in Bucks.

“It was formed to look for oil, I think, by taking pictures from the air,” says Newman. “Its founder went to the military at the start of the war. He took it to the Admiralty, the Air Ministry, the War Office and they said ‘no, what’s in it for us?’ It became massive once they realised what they’ve got and can get – 1,700 people at RAF Medmenham – and that’s an important intelligence story that’s not been told in fiction. Unusually, there were equal numbers of men and women at all levels.”

Books aside, where does Newman get his live material, I wonder?

“I walk around talking to myself, imagining saying it on stage,” he says. “You’ve got a sort of an idea, and it’s not funny yet, but as you talk to yourself when everyone else is out, you’re imagining you’re on stage and then it comes. Occasionally a joke comes straight away, or you see a funny thing. My big fear was that it’d be like being a mathematician. You know, they say, ‘Oh, we’ve done all our best work by 32’, or something.”

Happily, that’s not the case for Newman. “I just finished a live tour and the new stuff got some of the biggest laughs,” he smiles.

And that shows intelligence.

• Intelligence by Robert Newman (Profile, £16.99) is out now