Liam, 21, is doing time at Norwich prison for buying a stunt gun online ITV

The notion of a prison documentary often lends itself to the turmoil jailbirds are subjected to as they dwindle upon their crimes in a confined, stuffy space. But tonight's programme, Her Majesty's Prison: Norwich, explores how the affected families are the ones really living behind bars as they endure another kind of sentence when a loved one is banged up.

The latest film from ITV's prison series looks more into the torment of being separated from loved ones. We discover that families are torn apart as a fifth of prisoners' marriages break up, and the ones who are auspicious enough to hold their personal lives together are six times less likely to commit another crime.

Tonight's episode follows the acclaimed series that looked at life in HMP Aylesbury, Strangeways and Wormwood Scrubs, as ITV delves into the Norwich prison and examines how inmates cope with life inside a cage. The majority of the 2,500 prisoners who pass through each year are husbands and fathers, and the documentary will take a closer look at the wives and children who are left behind.

Inmate Nick gets to see his family during visiting hours at Norwich prison ITV

One example we'll see is Nick, who has been sentenced to 13 years for conspiracy to supply cocaine. His partner is currently supporting him on the outside as he has served just two years, but his motivations are running dry as he struggles being away from his young son.

He said: "Austin [my son] has grown up in here, he took his first steps in here pretty much in the visitor's hall. It's not new to him, he's been coming since he was one.

"Having seen what my family are going through, the hardness of it - the last year-and-a-half, two years, [I've] watched my little boy grow up from a weekly visit - it's not what I want."

Liam Poore, 21, who was sent to jail for the first time after purchasing a stun gun online without realising it's an illegal weapon, also expressed his feelings of being locked up. He said: "When you get chucked in a cell and the door is locked, that's when you realise that's your life for the next 10 to 20 months."

The emotionally disturbing footage captures a number of fights, tales of drugs and violence and plenty of tears, and also divulges the ways in which families keep in touch with their imprisoned relatives. It shows how regulation is enforced as each letter is checked for smuggled items including drugs and SIM cards and how every child, no matter what age, has to be searched before visiting.

Darren, a prison officer at the Norwich jail, said: "Children can be little carriers. They are only a couple of weeks old or sometimes days old and it's something we have to do because people do hide items on children and young babies - the nappy area is a big area."

Viewers will also look through the eyes of a reoffender as Rocky, a 30-year-old father of two, worries about the strains his sentence will put on his partner as he awaits a sentence after pleading guilty to conspiracy to supply heroin.

He said: "Sometimes I sit and wonder why she does wait for me, she's a good girl. I'm going to have sort myself out. I can't lose her and the kids - they're my world, do you know what I mean?"

Realising perhaps too late that he desperately wants to turn his life around, he adds: "I just don't want to be involved with the drugs world any more. It's a mug's game."

Her Majesty's Prison: Norwich, airs tonight (4 May) at 9pm on ITV.