One Friday night in 1955, Tony Hancock decided he’d had enough. He’d been recording Hancock’s Half Hour for BBC radio every week and performing his own show in the West End.

On this particular evening, he walked off stage and kept on walking without a word to anyone. He was due to record Hancock’s Half Hour the following day, but that evening one of the producers received a call from a friend who worked in airport security.

The friend said, “Is Tony doing the show tomorrow? I’ve got tickets to the recording.” Yes, the producer confirmed, he is. “It’s only,” the friend said, “that I’ve just seen him walking on to a plane to Rome…” Harry Secombe ended up standing in for Hancock for three episodes of Hancock’s Half Hour, with a final fourth show featuring them both.

For decades, those tapes have been lost – among 20 of the 103 episodes that Ray Galton and Alan Simpson wrote that were erased or chucked away by the BBC. But when actor and bibliophile Neil Pearson unearthed a stack of old radio scripts he found copies of all 20. The BBC has decided to re-record all of these lost classics for broadcast on Radio 4.

They’ve now reached the Secombe episodes – so the obvious choice to play Harry, who died in 2001, was his son, Andrew. But back in 1955, how did the producers decide to recruit Harry to cover for the missing Tony Hancock?

“They phoned my dad,” says Andrew, 63. “I suppose they chose him because he was a well-known radio voice – he was doing The Goons and he’d done Educating Archie. He agreed at the last minute – and the first script was written for Hancock so he had to deliver exactly Hancock’s lines.”

Although we’ll never hear the original broadcast and get a sense of how nervous, confident or how different to Tony Hancock Secombe Senior was, Secombe Junior plays the first show with his dad’s brio but all of Hancock’s little verbal tics and mannerisms.

“I found it incredibly difficult because it’s all in Tony Hancock’s rhythms – he sort of undercuts everything, whereas my dad was big and enthusiastic,” he explains. “But then, for the second and third show, Galton and Simpson started finding Dad’s voice – the second is about him buying a racehorse, ending up the jockey and winning the race. That really wouldn’t be a Hancock story.”

It’s not the first time Andrew has played his dad – back in 2000 he was cast as Neddie Seagoon in a 50th-anniversary Goons special. “Originally, I said no,” he recalls. “My dad was in hospital and when I went to see him, I mentioned it. He said, ‘Oh, you’ve got to do it. It’s such fun.’ I couldn’t argue with him and I’m very glad I didn’t because he was right – it was great fun.”

He pauses and looks away for a second. His dad didn’t get to hear it, he explains softly, as he died in April 2001. “They made me a disc, but I didn’t take it to him. He was in no fit state to listen to it, which was a shame.” Was it weird playing your own father? He smiles and shakes his head.

“With my dad, what you saw on stage was basically an exaggeration of how he was in real life. He came on stage at 90 miles an hour because, from his Army days, he was terrified of getting the bird, so the bags of energy meant nobody would dare interrupt him.

“I watched him for so many years – we used to spend every Saturday at the London Palladium and it was like my playground when I was a kid. I used to stand in the wings, watching, watching and watching.”

In fact, Andrew was the quietest of the sprawling, would never follow my father. I was quite shy and I wanted to be a journalist. boisterous Secombe brood – two boys and two girls, who are all now actors or writers.

“So they were a bit surprised when I went into the business,” he nods. “It was a series of accidents, really. I swore I Then my English teacher gave me a part in the form play – The Idiot. Why he chose me, I have no idea,” he grins. “I was terrified – waited in the wings for my entrance. Then I heard my cue, thought of Dad and stumbled on to the stage where I fell over, got a big laugh and I’m afraid I was completely hooked.”

He’s a little disappointed there’s only a short run of these shows – Secombe’s role came to an abrupt end when Hancock heard how well he was going down, hurried back to restake his claim and Hancock’s Half Hour returned to its original form – almost.

Andrew explains that they phased out Hancock’s trademark monologue at the top of the show when Harry played the part, and when Tony returned, they didn’t bother bringing it back. “So Dad left a little mark on every single Hancock after that,” he says, smiling with affection and pride.

The Missing Hancocks is on Tuesday 6.30pm Radio 4