The Thick of It star was found guilty of the offence in 2007 and sentenced to ten months in prison, reduced to six on appeal. He served just over three months.
Langham has maintained that he downloaded the 15 graphic videos as research for a character in Help!, his two-hander with Paul Whitehouse. He later revealed that he had been raped by a family friend when he was 8 years old.
Langham told The Guardian: "I feel like a lot of the time I'm talking I'm justifying myself but I'm very sorry that I offended people by what I did. And particularly sorry to have offended other victims of child abuse.
"That was the last thing I'd have ever wanted to do. And I'm really sorry that because of my thoughtless, wilful, arrogant behaviour, I created enormous difficulties for my wife and my children, who I would do anything to not hurt."
When asked if he knew that his actions were indefensible, Langham added: "I knew it was illegal. It was just hubristic and arrogant of me to think I'm above the law because I'm an artist.
"I thought after [I'd played the character], I'll reveal I'd researched it, and people would say gosh, you've taken this really difficult subject and done something amazing.
"I'll do this thing, and everyone will think I'm wonderful. I thought if I pulled it off, everyone would admire me. And I'm a slut for approval."
Langham's wife Christine has admitted to feeling "angry" towards her husband for being "so stupid" in downloading the images.
The actor was asked to give a speech at the Oxford Union in 2008, but the invitation was later withdrawn.
> Chris Langham's West End work 'no secret'
Watch Chris Langham talk to Pamela Stephenson Connolly on Shrink Rap below: