The 46-year-old actress, who plays police detective Sam Lomax on the Channel 4 soap, became firm friends with the Hollywood heartthrob after they shared the stage in the West End production of One Flew Over The Cuckoo's Nest in 2004.
She gushed about their stage snogs, telling Reveal: "Christian's an amazing kisser and yes, we used tongues!
"I was 36, I was dating a 26-year-old street performer so I'd peel him off me every morning and then go to work and snog the Hollywood movie star. It was just wonderful!"
Lizzie continued: "Every night we were like, 'Who's in the audience?' Burt Reynolds was in one night, I met Patricia Arquette, ate chips and drank Pinot Grigio with Cindy Crawford.
"It was the time of our lives. I was getting paid £1,000 a week and all I had to do was snog Christian Slater!"
The actress has now adapted to her job on Hollyoaks, in which she stars opposite Stephen Billington (her screen husband Danny Lomax) and James Sutton (John Paul McQueen).
"Now I get up every day at 6.30am, I'm in my car by 7.30am, I listen to a breakfast show on the radio. I've never listened to a breakfast show in my life. I've never had a routine," she admitted.
And she revealed how her off-screen friendship with her male co-stars often leaves people baffled. "We're a terrible threesome. People get very excited when they see us out together. They're like, 'Why are you out with your husband and your husband's lover?' It tends to confuse people," she said.
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