Here's Part 4 of our special interview series with Noel Thomas - a Welsh sub-postmaster who was wrongly imprisoned for stealing money.

After 20 years, he and a group of fellow campaigners won a legal battle, having proven that the Post Office's computer system, Horizon, was actually at fault.

Previous installments are available here:

Noel Thomas, Gaerwen sub postmaster on Ynys Môn, was found guilty of false accounting at Caernarfon Crown Court on 6 November 2006.

Even though Mr Thomas was innocent, he agreed to plead guilty in an attempt to avoid prison. But the judge, Mr Winston Roddick, sentenced him to nine months imprisonment anyway.

Following the verdict, Mr Thomas was greeted by a familiar face as he waited to for transport to Altcourse open prison.

“As it happened I knew the court usher in Caernarfon, as he also worked at Gaerwen industrial estate," he said.

"When I was sent down, the first thing he did was bring me a cup of tea.

"He didn’t even lock the cell door.

"He spoke to me until it was time to go and he then placed handcuffs on me - he looked after me."

Mr Thomas’s daughter Siân attended the court hearing, and was waiting to collect her father to take him home. She said she felt bereft when she heard the verdict.

“It was as though he was dead to be honest," Siân said.

"That’s all I received from the barrister, his coat and wallet.

"I wanted to return home to my Mother and not let her watch the television - I had sent a friend over to be with her.”

Siân said she was in shock for the duration of her journey home.

“I felt certain that he was coming home with me, but he wasn’t allowed.

"I held his coat and smelt it in the car. I remember walking through the door and my Mother asking: ‘where is he?’”

By this time Mr Thomas was in a lorry, which was making its way to Wrexham to collect more prisoners.

“They then told me in Wrexham that there was no room in Altcourse prison, outside Liverpool, and that they had to take me to Walton.”

Mr Thomas describes Walton prison as “a hell of a place.”

“It was 10 o’ clock at night when we arrived.

"I had a shower and I had to wear Walton clothes instead of my own.

"What was worse was having a shower with three other men watching you.”

Walton prison was very confined, and Mr Thomas was placed with a category of “right dodgy” prisoners.

He said: “I shared a cell with a ‘real rough man’ but he looked after me.

"He was from Liverpool, and into drugs. He spoke with me and helped me.

"It was as though you’d place a dog and a cat together in a cage – if they’ve never been in one before, they don’t want to be there.”

Mr Thomas recognises that he broke down when he was alone in his cell, around eight days before being sent to Kirkham Prison in Lancashire.

“This chap had to go to work in Walton and I was left on my own.

"I was only allowed out to get my food - I’d have half an hour on the landing at lunch time, and some time in the evening if we were lucky.

“At the end of the day, Kirkham was a better prison.

"There were around 20 of us together, and everyone had their own cell.

"They would open the door for you at 7.30 in the morning and lock you in at 7.30 in the evening.”

During the day, Mr Thomas would usually work in a glasshouse. There was also a vegetable farm, and a wood workshop where prisoners would make benches.

“When you arrived, they would assess you for three days to see where was best to send you, and I was sent to the garden.

"One of the inmates was an attorney from Manchester – a really lovely man - and he was given a job.

"His work there was to help prisoners to fill in forms or claim benefit when they went out.”

In prison, Mr Thomas’ weekly wage was £10.00, and he spent his 60th birthday behind bars.