With such tight filming schedules, the series was forced to hire a replacement, opting for 53-year-old ex-Dempsey and Makepeace actress Glynis Barber.
Earlier this week, producers revealed that 72-year-old Gascoine - star of The Gentle Touch and C.A.T.S. Eyes - had signed to play the role of Archie Mitchell's (Larry Lamb) estranged wife Glenda.
However, during her first day on set, Gascoine took the decision to withdraw from her filming commitments as she felt that she "lacked the right experience to film such a big continuing drama".
Speaking of her conclusion to step down, Gascoine said: "I was so looking forward to playing Glenda but having spent the last 15 years working in America - largely acting in single drama and writing fiction - I felt, on arrival, I lacked the right experience to film such a big continuing drama.
"I have tremendous respect for EastEnders and the cast so I didn't want to let the show or my fellow cast members down."
She added: "I'm really sad that I won't now play a part in EastEnders but I'd like to wish Glynis Barber the best of luck in the role of Glenda."
Barber - who portrayed the part of Harriet Makepeace in the 1980s crime drama and more recently Emmerdale's DCI Grace Barraclough - began filming with EastEnders earlier this week and will make her first appearance as Glenda in the New Year.
> Click here to read more about Glenda Mitchell