Appearing relaxed and confident, he is calmly discussing his plans to return to the stage after a 10-year absence, in Richard III in Sheffield next spring. No matter that three and a half years ago he doubted whether he would ever perform on stage again because, he said, "I would be too scared".

What a difference a few attained ambitions and a spell in Hollywood make.

"I think things go in cycles," he mused. "People have been after me for a long time about when I will do another play and go back to the theatre, and the answer was when I felt really excited about doing it. Now I do. Having looked at Richard III for many years now and having talked to various people about it, I suddenly realise I am very excited and it is something I am compelled to do."

It marks a return to his theatrical roots for the 40-year-old Belfast-born actor who, since joining the Royal Shakespeare Company in 1984 at the age of 23, has moved with relative ease between Shakespeare, television drama (Fortunes of War, in which he co-starred with his then-wife Emma Thompson) and Hollywood, where his recent work has included starring in Woody Allen's Celebrity, providing the voice for Miguel in the animated The Road to El Dorado and playing the evil Dr Loveless in the embarrassing The Wild, Wild West.

Perhaps not surprisingly given this choice of films, it is his Shakespearean films that have been best received. Since winning Oscar nominations as both Best Actor and Best Director for his 1989 Henry V, he has directed movie versions of Much Ado About Nothing, Hamlet and Love's Labour's Lost.

But now he feels that cycle has ended. In the past few months he has been indulging his desire for variety and fresh challenges by playing SS General Richard Heydrich in the television drama Conspiracy (broadcast on BBC2 this autumn), for which he received an Emmy nomination; taking the title role in the biographical drama Shackleton about the Antarctic explorer Sir Ernest Shackleton (to be shown on Channel 4 early next year); and starring in director Philip Noyce's film Rabbit-Proof Fence (also scheduled for next year), the true story of three Aboriginal girls who were taken away from their families in 1931 as part of an official Australian government policy.

We were talking during a brief stopover he made in Los Angeles on his way back to England from a trip to New Zealand. "It was just a holiday - I don't talk about my private life," he said with a smile, doubtless mindful of the unwanted publicity he attracted with the 1995 break-up of his marriage to Emma Thompson and his subsequent four-year relationship with the actress Helena Bonham Carter.

His close-cropped hair is back to its natural reddish-brown, having been dyed blond for the Heydrich role - "I got rid of the man by washing him out of my hair," he said - and he was looking well rested and was, he said, eager to return to work.

Before turning his attentions to Richard III, however, he has a very different stage commitment to fulfil. He will be directing The Play What I Wrote, a tribute to Morecambe and Wise which opens at the Liverpool Playhouse on Thursday and is expected to transfer to the West End.

"I've always been a big fan of Morecambe and Wise and when I was 14, I wrote to them to ask if I could get tickets for their Christmas show," he recalled. "I couldn't, but they sent me an autographed photo instead."

One of the running gags in the Morecambe and Wise Show was that Ernie Wise boasted of writing a play very quickly and referred to it as "the play what I wrote".

The comedy duo the Right Size - Sean Foley and Hamish McColl - wrote The Play What I Wrote about two comedians who are asked to do a tribute show about Morecambe and Wise. The last 20 minutes of the play will feature the classic skit and each evening there will be a surprise celebrity guest.

"Morecambe and Wise were such a great combination of silly humour, fantastic warmth and pathos," said Branagh. "The two lads from the Right Size have often been compared to them as being very silly, funny and benign, so I knew about their work. They approached me because they wanted somebody to direct it who was keen on Morecambe and Wise and had some history in comedy. I'm looking forward to it very much. It's a very funny script. They've managed to invoke Morecambe and Wise without impersonating them."

And the guest stars? "They're being kept secret," he said. "Our plan is that each night we will have a surprise guest star because one of the features of the shows was that Morecambe and Wise had a guest star come in and be in one of the plays what Ernie wrote. I think there'll be a lot of genuine surprises."

While The Play What I Wrote will be a singularly British venture, Branagh is currently receiving much praise in America for his portrayal of Heydrich in the HBO cable television production of Conspiracy, an account of the Wansee Conference on January 20, 1942, at which 15 high-ranking members of the Third Reich enjoyed a sumptuous meal while matter-of-factly putting into motion a plan to kill 11 million Jews as part of Hitler's "final solution".

"You've got this group of seemingly ordinary civil servants speaking in a tone and manner that is utterly chilling," said Branagh. "I read the script with horror because of the casual way in which mass destruction was discussed."

Conspiracy was filmed mainly at Shepperton, where the room at Wansee was duplicated. "There was a terrible feeling of claustrophobia and suffocation on set," said Branagh. "There was something about the Nazi uniforms that was creepily effective. Once those jackets were on, the doors were closed, someone said 'action' and you started performing in this low-key way, you were struck very terribly by the fact you were re-creating something that had really occurred.

"As soon as there was a break in filming a lot of the actors would take their Nazi jackets off and go outside just to get away from the atmosphere of it."

Equally demanding but in a very different way was Shackleton, which he finished filming a few weeks ago. "We shot in the Arctic and spent about six weeks on an icebreaker in the middle of the Arctic Ocean, shooting on ice floes that wouldn't behave themselves. Occasionally we had to get off the ice very quickly as it broke up underneath us. We were very, very cold and it was physically very challenging but it lent terrific authenticity to the piece."

Now, yet another cycle in his life begins as he turns his thoughts to the stage - not just Richard III at Michael Grandage's Sheffield Crucible but also the RSC, with whom he has been having talks with a view to returning there. "The last time I acted on stage was with the Royal Shakespeare Company in Hamlet 10 years ago," he said. "Now I'm motivated to do it again."