John Simm has said he had a real insight into what it must be like to be locked up while filming his latest drama.
The former Life On Mars and Doctor Who star plays prisoner Ian in Everyday, directed by Michael Winterbottom.
The feature-length TV movie focuses on how a man's prison sentence affects his family and was filmed on location in real prisons.
John said: "People say it's cushy being in prison, and it certainly isn't from what I saw. It's no picnic at all.
"And being wrenched apart from your family, there's nothing worse than that.
"And for it to be your fault as well is an awful thing to carry around and try to make right in these little pockets of time you've got together."
John said: "All the prisoners I talked to, when I asked what the worst experience was, said it was when the door shuts for the first time in your cell.
"And you look around your tiny room and you think, 'Oh my God, what have I done?'."
:: Everyday is on Channel 4 on Wednesday, November 14.