Colin Firth said he was relieved only to be playing at being king in his new film, as he found it "strange".
Colin - who plays King George VI in The King's Speech, about the monarch's battle to overcome his stammer on succeeding the throne - insisted the pressure of being a public figure bore no relation to his own life as a celebrity.
Colin said: "I don't know what his life must have been like - I don't have the restrictions on my life, I don't have the protocols. And I don't have to answer to people who have constitutional power. It couldn't be more different."
"And it was a very strange sensation even to act - walking down a corridor where certain people bow their heads."
The 50-year-old star of Bridget Jones, Love Actually and Pride And Prejudice was greeted by screaming fans as he arrived on the red carpet at the American Express gala screening of The King's Speech at the BFI London Film Festival.
The film, directed by Tom Hooper and starring Helena Bonham Carter as King George's wife the Queen Mother and Geoffrey Rush as his speech therapist Lionel Logue, won the People's Choice Award at the Toronto International Film Festival and is tipped for Oscar success.
Colin said of the awards buzz: " Of course it's encouraging. You can't really answer any questions about but all you can say about it is it's had two screenings and it's a great start."
The King's Speech will open in cinemas in January.