Michael Gambon will play Winston Churchill in an upcoming thriller.

The 74-year-old actor - who is renowned for his role as Dumbledore in the 'Harry Potter' movie franchise - will take on the part of the war time Prime Minister in the upcoming spy picture 'Target Churchill', reports The Sun newspaper.

The film - written by Warren Adler and biographer James C. Humes - has a fictionalised plot which follows an attempt by Soviet leader Joseph Stalin to have Churchill assassinated before he can make his famous Iron Curtain speech in 1946.

The news Gambon is to take on the iconic role follows the actor's decision to give up his career in the theatre.

The 'Casual Vacancy' star confessed his fading memory has left him with no choice but to stop taking on roles in plays and focus on his television and film career instead.

He said: ''It's a horrible thing to admit, but I can't do it. It breaks my heart.''

Told his memory still seems quite sharp, he added: ''Yes. But it's when the script's in front of me and it takes me forever to learn it. It's frightening.''

Although he insisted he has no plans to retire just yet, saying:''No. You've got to go to work, haven't you?''