The Archers icon: 'Wendy Richard and Angela Rippon thought I was the sexiest man in showbusiness'

He actually goes back a year earlier: "I was a crooked decorator, Dave Escott, who had a flirtation with Peggy. Producer Tony Shryane said, 'We'll get you back!' and three weeks later my wife [Judy Bennett, who played Shula] came home and said, 'You're in!'

"I was overjoyed. Got the first episode, went for lunch, ran into Jack Holloway who played Ralph Bellamy. He was in a bad mood, saying, 'I've just been written out of the bloody programme!' Then back in the studio the others said, 'Oh yes. You’ve bought his farm.' No wonder he wasn’t pleased to see my ugly face!"

In 1976, Brian married Jennifer, and took on her children by two fathers (she was the serial's first scandal, a gesture to the free-love 1960s). "It was interesting, because in real life, I had proudly taken on Judy’s two little boys, Toby and Barney. Her real first husband was a Brian, and my first wife a Jennifer. How about that?"

Collingwood is the jolliest company, and relishes his character's adventures, which go beyond the tweed-capped practicality of farming. After a couple of years, the new editor, William Smethurst, told him he’d decided to turn Brian into a womaniser. "I suppose because it was me, he spotted a little bit of – er – Leslie Phillips naughtiness" (cue a stagey twinkle). "He wanted a bit of daring humour. Well, it kept me in the show for 50 years."

Hence Brian’s fling with posh Caroline Bone and flirtation with the flame-haired Pony Club temptress Mandy Beesborough. Another new editor, Vanessa Whitburn, told him, "Women of a certain age always ask me, 'When will Brian have an affair?'" That became his explosive love affair with Siobhan Donovan, who died young and whose son with Brian, Ruairi, was taken on, heroically, by wife Jennifer. Collingwood loved it. "The joy of continuing drama on the radio is that we play to real time: this affair lasted jolly nearly three years."

Passionate scenes with Caroline Lennon had their problems: "At the peak I was just out from a hip replacement. There I was, wincing from post-op, manipulating reading glasses and a script, and there’s somebody beside me rustling the sheets. Taxing."

It had its effect, though. At Wendy Richard’s 40-years-in-showbiz lunch, she told him, "Angela Rippon and I think you are the sexiest b*****d in showbusiness!" "I went home after a few glasses of wine – Judy was ironing – and proudly repeated the line. Her reply was: 'Only in showbusiness!' That’s a good marriage."

Brian twinkled on, with more plotlines: criminally charged with polluting the River Am, he had to downshift from the grand farmhouse, while (with unaccountable devotion) letting his woo-woo stepdaughter Kate keep her "spiritual wellness" yurt field.

His scenes with Hollie Chapman, as Brian took his alcoholic daughter Alice to rehab, were genuinely wrenching, all fatherly fear and gentle humility. "I hope so. When Brian turned into a real womaniser I said, 'Delighted! Yes, there are men like that. But please don’t make him a one-dimensional dirty old man. Make him a good father, see the charm in him. And with scenes like that, or the death of Jennifer, you’re aware that a lot of people are going through it, so it’s important to get it right."

I do wonder how, after five decades, Collingwood feels about the ever-loosening sexual mores of Ambridge: from Brian’s adulteries to Ruairi’s foray into sex work. “Yes, the world changed. I remember David Blunkett in the 90s first going on about all this, and thinking, ‘Well, we’ve changed and we’re quite successful. Time the Labour Party changed and it might be successful, too.’ Then along came Tony Blair!”

The Siobhan affair did create a long, intense scene – when Brian’s stepdaughter Debbie discovered his betrayal of Jennifer – that Ned Sherrin once said was “like Chekhov”. That scene was special to Collingwood because Debbie’s played by Tamsin Greig, now rarely heard in The Archers (“she’s got so famous Debbie had to move to Hungary”). “We had many scenes together. I find her a remarkable actress and human being.”

Collingwood’s a veteran, worked in rep and shared a study at school with Richard Eyre. He’s especially intrigued by widower Brian’s latest conquest. “I am having a brief encounter with Miranda. Lucy Fleming who plays her is the daughter of Celia Johnson from Brief Encounter – how about that! She sounds like her, too!”

He gets on fine with Brian’s rival, Justin, played by Simon Williams: "Wonderful hair. I said, ‘If I had silver hair like yours I’d be a major film star’. He said, ‘Mmm… takes more than the hair, darling!'"

In his private life in Hampshire, does he mix with Brian’s real-life equivalents – harrumphers of mature years? "Hordes of them. It's very naval down there, so it helps that I’m related to Nelson’s Admiral Collingwood. One plummy chap asked if I’d come down to retire? I said, 'No, darling, I’ve been semi-retired ever since I left RADA!' I think it was the first time any man had called him darling."

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