The comedy Cleo, Camping, Emmanuelle and Dick also reveals that the filming of the Carry On series was a less than glamorous affair, characterised by leaking caravans, inadequate pay-cheques and argumentative co-stars.

Most of the play's action takes place on rain-soaked locations with a scantily-clad Barbara taking refuge in Sid's trailer while he and co-star Kenneth Williams carry on their notorious feud, which began when they starred together in the TV series Hancock's Half Hour.

Windsor: gave support to the project

Windsor, who is now enjoying acclaim for her role as Peggy Mitchell, landlady of the Queen Vic, in EastEnders, has given her full support to the production after meeting Terry Johnson, the play's director and author.

She read the script, suggested a "few little tweaks" and advised Johnson to find an unknown actress to play her. The role eventually went to Samantha Spiro, who is said to give an "eerily convincing" performance.

Windsor herself has fond memories of the Carry On days. "We didn't get a lot of money and we did always seem to be doing outside shots in winter," she said in an interview with The Observer, "but it paid the mortgage and I loved it."

She admits to being nervous about seeing the play for the first time at its opening night on Monday, and says several people have expressed their amazement that she allowed the play to go ahead.

Affair kept secret

However, she is completely open about her three-year love affair which was conducted whilst she was married to her first husband, the gangster Ronnie Knight.

James, who was also married, had a reputation as an inveterate womaniser with a roving eye to rival any of his famously lascivious Carry On characters.

Windsor said she managed to resist his advances until the pair appeared in revue and were "thrown together" while on tour.

Airing dirty laundry: the play exposes the truth behind the Carry Ons

The comedian, who was 25 years older than Windsor, told her: "I've got about 10 years left and I want to spend them with you."

However, despite being tempted to leave her husband - who never suspected her involvement with James - she finally put an end to the affair.

"I cut Sid out of my life. It was the only way I could stop it," she said, expressing regrets that they were never to speak to each other again.

James died in 1976 at the age of 63 and Windsor can clearly remember receiving the news: "The first thing I did was ring Ronnie (her husband) and say 'You have to come home.' Then I just went to pieces. I remember Ronnie saying, 'Blimey, Barbara, I hope you cry like that when I go.' If only he'd known."