Image copyright Reuters Image caption Downey Jr is currently promoting Avengers: Age of Ultron, in which he plays superhero Iron Man

Actor Robert Downey Jr has spoken for the first time about walking out of a UK TV interview earlier this month.

Quizzed by US DJ Howard Stern, the Avengers star dubbed Channel 4's Krishnan Guru-Murthy "a bottom-feeding muckraker" for bringing up his past problems with drugs.

The actor said he had been "promoting a superhero movie" and suggested his interviewer had a "creepy dark agenda".

Guru-Murthy himself has insisted he had "no particular agenda".

Writing in The Guardian, the broadcaster said Downey Jr's "PR man" had been informed the actor's "recovery from jail and drug abuse" would be brought up in the interview.

"We don't do promotional interviews on Channel 4 News," Guru-Murthy wrote.

"We agree with PR people that as well as talking about a new movie for a while we want to ask wider ranging questions on relatively serious topics."

"Social decorum"

Downey Jr, however, said Guru-Murthy had been "weirding [him] out" with his "weirdo" line of questioning in his "first interview of the day".

He said he now wished he had left the interview sooner and suggested the Channel 4 newsman had violated "social decorum" by scrutinising him like "a kiddie fiddler who's running for mayor".

He said he needed "to distance myself from this clown".

"Otherwise, I'm probably going to put hands on somebody, and then there's a real story," he added.

Guru-Murthy previously clashed with director Quentin Tarantino, who bridled when asked to discuss the violence in his film Django Unchained.

"I know he pulled the same garbage on Tarantino, and Tarantino stayed in his chair and lit him up for five minutes," said Downey Jr of that 2013 encounter.

"I'm a 50-year-old guy, I used fancy words... and yet I'm completely unevolved when it comes down to simple boundaries."

The actor is currently promoting fantasy sequel Avengers: Age of Ultron, in which he can be seen reprising his role as armour-plated superhero Iron Man.