Katherine Kelly knew she wanted to play Lee Middleton (Kenny Everett's wife) in the BBC Four biopic Best Possible Taste: The Kenny Everett Story within a few minutes of starting Middleton's autobiography.

Says Katherine: "I was fortunate to be sent a lot of scripts when people knew I was leaving Coronation Street, but this one stood out a mile.

"Before the audition, I wanted to see if I felt I could play this woman and there wasn't any footage to watch as Lee kept herself out of the public eye and was not nearly as well-known as Kenny. Nowadays, we tend to know a lot about the wives of celebrities and are very aware of them, but Lee didn't want to play it that way. She had been Billy Fury's girlfriend for seven years and she was very much her own woman but wasn't interested in the fame.

"So I bought her autobiography second-hand off Amazon and within the first seven pages I felt like I knew Lee. She's the same age as my grandma, born 10 miles away from where I was born. We even share things like this real tomboy element - I could go on because there were loads of little things that just made me feel 'wow, that's just like me'. I felt a real connection with Lee, and a great admiration for her, and felt strongly that I wanted to play the part."

And Katherine was over the moon to land the role despite being on stage at The National Theatre while filming Best Possible Taste: The Kenny Everett Story.

"It was tricky and I knew the timing wasn't ideal, as I was also on stage eight times a week in She Stoops To Conquer. I'd be getting up at 4am to film and then be on stage until 10:30pm but I was overwhelmed with a desire to do it.

"Thankfully, the team were prepared to make the dates work because it was difficult for them having an actress who has to be cleared by 4:30pm every day to get on stage. But I'm really pleased they made it work because the best people were involved in this project, and everyone believed in it, which made for a wonderful atmosphere.

"I didn't find it a problem switching from one character to another from stage to screen. I'd been working on the play since December, so that part was embedded in me when I started filming Best Possible Taste. It was just the tiredness in general; it's quite hard existing on five hours' sleep a night, but I guess I was no stranger to that with the schedule I was used to on Coronation Street!"

Meeting Lee for the first time was a memorable experience for Katherine. She explains: "The associate producer, Luke Franklin, knew Lee well as he'd been working on this for two years, so he organised for me to visit Lee and her husband John at their home in the country. I went for lunch and stayed nine hours! I was supposed to be going to the theatre that evening but cancelled because I was having such a great time poring over Lee's scrapbooks and memorabilia; she's kept everything. Like me, she's a real hoarder. We were listening to all her old records and just got on like a house on fire. They'd seen the audition tapes and were pleased with my casting. John thought I captured Lee's soul and emotion, which meant a lot."

So did Katherine feel any burden portraying a real, living person?

"The thing about Lee is there is so much to know. She's lived so many different lives and has so many stories to tell, but this is Kenny's story and about them as a couple not Lee as an individual.

"I wanted to do Lee justice but she didn't have a public persona as such, therefore I haven't got the responsibility that Oli has, because people have expectations of the way he's going to play Kenny, as they remember him so vividly. I'm starting afresh with Lee to a 2012 audience.

"I did feel pressure because I wanted to do justice to Kenny and Lee's story. Lots of people presumed it was a cover up and it absolutely wasn't in any way. So I wanted to get the real message across. This film tells you why they got together and about their relationship. They really did come together and get married for love and it is an unusual story; people find it hard to accept that you can fall in love with the person and not their sex. It's a very interesting and modern love story that continues to be discussed and debated."

Katherine is well used to the rigours of hair, make up and costume changes, appearing in a restoration comedy at The National Theatre, but how did she cope with Lee's look in Best Possible Taste: The Kenny Everett Story?

"It always takes longer for the girls to get ready and for this role I had a sixties, seventies and eighties wig, and I think I wore a different outfit in every single scene! I had about eight hours of costume fittings beforehand, and so many clothes that we needed to find because Lee was a bit of a superstar in the sixites when we first see her; she was rock and roll. She had separated from Billy Fury and she was the It girl of the time. It wasn't like she was a wall-flower - she was the woman: best mates with John Lennon's wife, leader of the pack in terms of the girls.

"She goes through a real journey and becomes a hippy during the seventies, when she is at one with the world, lives on a farm, rejects drugs and finds a spiritualism that takes her through to now. Then she meets her second husband, John, in the eighties and has this whole Dallas vibe going on. It's been a really thrilling part for me. Even if Lee had just been a couple of scenes in the film I would've have wanted to be part of it."

Talking of her co-star Oliver Lansley, who plays Kenny Everett, Katherine says: "Oli is such a talented all-round performer and such a lovely individual. Lee and John came to watch us film their wedding scene and even though Lee had met Oli before he made her cry because, she said, it was like being back in a room with Kenny. This was a very special job. Plus I have always loved those BBC Four films and I am so glad I got the chance to be in one."