Police are thought to have already ruled out foul play.

Last year Ledger revealed he had been taking sleeping pills, which reportedly cause side effects in some patients.

The actor had trouble sleeping while filming the latest Batman movie The Dark Knight. He played The Joker, a character he described as a  "psychopathic, mass-murdering, schizophrenic clown with zero empathy".

"I probably slept an average of two hours a night," Ledger told a newspaper. "I couldn't stop thinking. My body was exhausted, and my mind was still going."

COWBOY: Ledger was propelled to fame after starring in Brokeback Mountain

He said he took two Ambien pills which didn’t help him sleep for more than an hour.

Australian Prime Minister Kevin Rudd paid tribute to the actor for delivering “some of the greatest performances by an Australian actor.”

Tributes to the 28-year-old Brokeback Mountain actor flooded in from actors and directors as neighbours in the Soho area of Manhattan described him as “sweet” and “a loving father”.

Mel Gibson said Ledger’s death was a “tragic loss” and added: “I had such great hope for him.”

Heath starred as a jousting champion in comedy A Knight's Tale

The actor, who played Ledger’s vengeful father in The Patriot, said: “He was just taking off and to lose his life at such a young age is a tragic loss.”

British actor Martin Ballantyne, 35, from Norwich, met Ledger when he worked as an extra in The Dark Knight, playing one of The Joker’s henchmen during filming in London last autumn.

He described the star as a professional figure who remained in character while on set, but was happy to share a joke and a cigarette with lesser lights once the work was done.

The body of the Australian actor was removed from his home last night

“I spent 14 hours with him on set so we got talking,” he said, “we had a cigarette together but I didn’t want to be too friendly because he was the big star.

“I can’t really remember what we said, it was just small talk, how are you, that sort of thing, but he seemed very pleasant. He wasn’t like a normal guy, I mean he’s a big star, but he was a very nice bloke.

“He was in character all the time on set, like a method actor he didn’t really switch off between takes, he wasn’t friendly and chatty while he was working.

Ballantyne added: “He didn’t seem troubled. I know he was having problems with his marriage at the time, but I only found that out afterwards.

“I was very, very shocked when I found out about his death. I’d always admired him as an actor and I jumped at the chance to be in a film with him.”

Ledger won Oscar, Bafta and Golden Globe nominations for Brokeback Mountain - during the filming of which he met Williams, a co-star, on set.

He also starred in a number of other smash films, including teen film 10 Things I Hate About You and comedy A Knight's Tale.

Ledger played the suicidal son of Billy Bob Thornton in Monster's Ball and had a starring role in The Patriot.

His latest film The Dark Knight is set to be released this summer. Ledger was cast as the Joker in the high profile Batman epic - a role tipped to cement his status in Hollywood.