Dame Helen Mirren worries about continually playing royal characters – but would make an exception for one who was “very fat”.

The actress won a number of accolades for her portrayal of Britain’s Queen Elizabeth II in 2006 movie The Queen, including the best actress Oscar.

She is playing the royal again in a new London theatre production and admits fearing she was being typecast.

With that in mind, there is still one other monarch she would give anything to star as on screen.

“I would love to play Catherine the Great of Russia, in her later years. That’s an extraordinary character and I could eat as much as I liked, because she’s very fat,” she told the BBC.

Helen spent a great deal of time researching Elizabeth before shooting The Queen and rehearsing for the play called The Audience.

Watching documentaries about the monarch helped her as she was able to practice her mannerisms.

“There is a physicality about the queen that is very distinctive. I watched a lot of film – thank God for YouTube,” she laughed.

“I watched the documentaries that the rest of us have watched, but I watch them in a particular kind of way – seeing little moments.”

Although many would expect her to focus on modern footage, when preparing for the film Helen went further back. The movie follows the royal in the time following the death of Princess Diana in 1997, but the actress felt she had to understand all the queen had been through from childhood in order to do her justice.

“When I did the film I found myself only watching film of her before she was queen, up to the coronation [held in 1953],” she explained.

“I wanted to see the person she was before this mantle fell upon her, and just see who the 13-year-old was.”