The 75-year-old said “the time has come for me to hang up Charlie’s scrubs after the most wonderful 37 years” starring in nearly 900 episodes of the much-loved TV programme.

The BBC said Thompson will be filming until autumn, with his final scenes airing next year in the “culmination of a gripping exit storyline which will see the character front and centre of the action”.

Thompson said: “A real nurse – Pete Salt, inspired Charlie Fairhead.

“Together with the writers and producers, I have tried to bring to Charlie the compassion, kindness, heroism and sound judgment that we all see and love in Pete, and I want to say thanks to Pete and everyone else over that time who has inspired me in bringing this character to life.”

Thompson’s character has played a “central part in the show” since it launched in 1986, as the “lynchpin of the hospital’s emergency department” and at the centre of “countless major storylines which explored challenging and thought-provoking subjects”, the BBC said.

Jon Sen, executive producer of Casualty for BBC Studios, said: “Derek and I would often joke that, after such a long and dramatic career in the NHS, there was almost nothing that Charlie hadn’t seen.

“So it was an amazing surprise to me when Derek arrived with a brilliant idea for Charlie’s exit as part of an upcoming storyline, which was too good to pass up. We will all miss Derek enormously.

“Over nearly four decades, Derek has crafted an iconic character who is woven into the fabric of British TV history.

“We will miss his craft, his humour and his on-screen presence. We’re also going to miss a friend, so for the next few months we’re going to have a ball filming Charlie’s final chapter.”

During his time on the show, his character was run over by an ambulance on his wedding day, suffered a near-fatal cardiac arrest during a gang siege, and saw the “heart-breaking farewell” of his loving relationship with fellow nurse Duffy (Cathy Shipton).

In 2017, the actor was the top earner in the scripted TV (drama and comedy) category, earning between £350,000-£399,999 and ranking above stars such as Danny Dyer and Peter Capaldi, according to figures from the BBC’s annual report.

The BBC said details of Thompson’s final Casualty storyline will be revealed “in due course”.