Warning: Contains offensive language

Rob was often the last prisoner into the visitors’ room.

On one of Alison’s previous attempts to see her son, he hadn’t turned up at all. The officers simply said they couldn’t find him.

Now she was here again on one of the hottest days of summer 2016. The room - big enough to hold 40 tables - was sweltering.

Alison and her husband Chris sat down in the middle of the room - waiting and watching intently. A single file of inmates queued - each was methodically patted down before coming in. Alison didn’t look away for a second - she wanted to see Rob the moment he arrived.

Despite his distinctive close-cropped red hair, it was sometimes hard to make him out among the identical blue and white check shirts worn by the other prisoners.

But this time he was unmissable. Every visitor turned to see Rob enter the room.

“He was walking like a zombie with his back arched, completely out of it. I was absolutely shocked,” his mother recalls.

Alison leapt up and ran to Rob. Chris, who was queueing for coffee, also rushed to his son. Rob looked on the verge of collapse.

Chris called his son’s name, says Alison. “Rob said, ‘Is that you, Dad?’”

They brought their son over to where they were sitting. “I was shouting, ‘Can somebody come and help us?’” says Alison.

As Rob sat down, she noticed that he had a T-shirt on underneath his prison-issue top - two layers despite the heat.

Alison wanted to cool him down.

“As I pulled the T-shirt down I noticed that he had ‘twat’ drawn across his chest in Biro.”

Alison shouted again for help from nearby prison officers. The medical team escorted Rob out of the visitors’ room and checked him over.

They denied he was under the influence of Spice, but his mother was convinced.

“It was obvious he’d taken it, we know he had. I was scared for him and I felt that he was humiliated.”

Also in the visitors’ room that day was Ben, an inmate who had served time in six prisons and was then inside after a fraud conviction.

He was talking to his girlfriend when Rob entered the room. “I’d seen Robert about, always dazed, high all the time.”

Rob and Ben were being held on the same wing. But it was only after seeing the episode in the visitors’ room that Ben got to know Rob.

“He came in doubled over backwards as if he was going to fall over, sweating.

“When the parents sat down I told them, ‘I’ve seen him on my wing, I will keep an eye on him.’”

Rob had been transferred to The Mount prison on 11 May 2016 at the age of 24, after serving a large part of his sentence in HMP Peterborough.

It marked one of the final stages of a sad decline.

He had been someone that people loved. One friend would later describe his “wildly engaging smile and his eccentric sense of humour”. Another wrote: “Swimming in the park on boiling hot days will always stay with me, as will making dens and climbing trees - always in places we shouldn’t.”

But Alison had seen a big change in Rob in his penultimate year at secondary school.

Previously a sporty child, playing rugby and cricket at county level, he and his friends then started to smoke cannabis. The drug was supplied by one friend in particular.

“He was able to supply them with whatever they wanted and they were impressionable.

“A lot of his friends got through that stage but for Rob, I realise now, from the age of 18 it affected his mental health. That’s when his behaviour became quite unpredictable.”

There is evidence that cannabis can have an effect on teenagers’ mental health. A 2015 study by King’s College London found that the risk of psychosis was five times higher for those who smoked potent cannabis every day compared with non-users.

Rob didn’t seem built to cope with addiction.

In his early 20s he travelled to India three times. He had always been interested in the spirituality of India - but his mother thinks he was really just trying to escape from his addiction.

On one of his trips he had to be picked up from Dubai airport by his father.

Rob had experienced a drug-induced breakdown and was in custody after stealing alcohol from an airport shop.

In the year before being sent to prison in the UK, his alcohol and drug addiction led to a string of shoplifting offences and then robbery.

One evening in November 2015 he demanded money from a man leaving a supermarket. When the man refused, he punched him in the face.

Rob was arrested and pleaded guilty to attempted robbery and theft. He was sentenced to 21 months in prison for those offences, with another three months added from a previous suspended sentence.

Alison says Rob was drunk at the time of the robbery and on anti-psychotic medication. He was full of remorse although he had little memory of exactly what he had done.

Rob was classed as a vulnerable person on entering prison because he had previously been diagnosed with schizophrenia and psychosis.

“He finally was sent to prison after he had been diagnosed with a mental illness,” Alison says.

“As his family, we were relieved, thinking the prison system will sort this out now.”