Robert Downey Jr was joined by an all-star cast at the European premiere of his new film, Sherlock Holmes: A Game Of Shadows, but the leading man admitted he would make a lousy detective.

The US actor reprises his role as the famed sleuth in the crime caper - the sequel to 2009 box office hit Sherlock Holmes - which sees his character reunite with friend Watson to battle criminal mastermind Professor Moriarty.

Robert braved the rain outside London's Empire Leicester Square with director Guy Ritchie and co-stars Jude Law (Watson), Jared Harris (Moriarty), and Stephen Fry, who plays Holmes' older brother Mycroft.

Despite portraying Sir Arthur Conan Doyle's beloved creation with gusto, the former hellraiser said he would never hold down a position as a private eye.

"I wouldn't keep the job. I tend not to exhaust myself thinking about details. I like to be creative instead," he said.

But Robert said the film - which also features Noomi Rapace, star of Swedish film The Girl With The Dragon Tattoo - was not a typical detective drama.

"It's not (TV crime show) CSI. It's about the way that people think, the mistakes they make and the things that Holmes picks up on. It's a character-driven mystery," he added.

The star also found himself dressed up in drag for one sequence in the film. "I'm not a very pretty lady, I'll tell you that much. I thought I'd turn into a female pretty easily, but I looked more like if my sister was on steroids," he said.

Director Guy said of Robert: "There are a lot of correlations between Sherlock Holmes and him, they both sort of dance on that thin line between madness and sanity and there is no other American male actor I know that has the drawl so perfect, a flawless English accent."