The 53-year-old Oscar-winner said spending so much time abroad has made him feel less British, reported Daily Express.
"I've never felt entirely English really, I've never felt that I quite fitted in and in some ways perhaps that's why it happened. You put on a mask and an identity fits all too well. I might be like one of those expatriates who seems more British than the people who actually live in Britain," Firth said.
"I might have taken on something of a pastiche where all the real English people have moved on and don't walk and talk like that at all," he added.