Andrew Secombe, the son of the late Harry Secombe, has joined the cast of The Missing Hancocks, the Radio 4 series in which lost episodes of Hancock's Half Hour are recreated.

Andrew, who is an actor himself with a credit list including Good Omens and Dirk Gently's Holistic Detective Agency, will take on the roles his father played in the original programmes.

This casting news has just been revealed, as Andrew has taken to the stage at the BBC Radio Theatre tonight alongside Kevin McNally, Kevin Eldon, Simon Greenall, Susy Kane and Robin Sebastian to record the first episodes in Series 3 of The Missing Hancocks.

Hancock's Half Hour was on Radio 4 from 1954 to 1959. In the second series of the show, which aired in 1955, Harry Secombe was drafted in at short notice to cover for Tony Hancock, who had walked out of a theatre performance and headed to Rome suffering from "nervous exhaustion".

Secombe, best known for his parts in The Goon Show, covered for Hancock for three episodes, before Hancock resurfaced in time to record the fourth episode. Writers Ray Galton and Alan Simpson changed the script of this episode so that, as part of the show, Tony Hancock went to Wales to thank Harry Secombe for filling in, with Harry appearing as himself.

True to the originals, Andrew Secombe will play his father's version of Hancock in the first three episodes of the new series of The Missing Hancocks. In the fourth, listeners will then hear him take on the role of his father whilst Kevin McNally, who has played Hancock in the recreations to date, will return the central role.

The episodes from the second series are missing from the BBC archive, so exist in only the form of the scripts re-discovered by actor and producer Neil Pearson. Speaking about the episodes, Andrew Secombe says: "These programmes have long been a source of curiosity among the family, developing an almost mythic quality - indeed I had no idea that the scripts still existed until I got the call from Neil Pearson! I'm thrilled to be a part of the very talented team bringing these episodes of a much-loved series back to life. Who'd have thought taking over the family business could be such fun?"

Radio 4 commission Sioned Wiliam says: "It's particularly delicious to have Andrew stepping in to his father's shoes. And a joy to welcome these great scripts by Galton and Simpson and Neil Pearson's meticulous production back to Radio 4."

Series 3 of The Missing Hancocks will be broadcast on Radio 4 in 2017. The episodes being recorded tonight and tomorrow are A Holiday in France, The Racehorse, The Crown Jewels, A Visit To Swansea and The Three Sons.

Once Series 3 has been broadcast, it will leave just five missing episodes. Radio 4 is expected to commission a fourth series of The Missing Hancocks next year to ensure these remaining episodes are re-recorded too.