At primary school Mikey did nothing - or worse. He found learning painfully difficult. He was laughed at as he struggled in class. “But at playtime it was different when I was smashing them and jumping on their heads,” he says. “They were so cheeky, I’m not really sorry for what I done. I think they deserved it - every one of them.”

He only discovered he was dyslexic when he was doing time at Polmont Young Offenders’ Institution in Falkirk. Mikey is 17 now, and one of the prisoners who contributes to a Channel 4 documentary, Dyslexic Criminals, to be shown next Monday at 8.30pm. The film is a low-key, but powerful, indictment of schools’ and prisons’ persistent failure to diagnose and help dyslexics.

The core of the documentary is a startling piece of research, conducted at Polmont by Gavin Reid, a psychologist and senior lecturer in the faculty of education of Edinburgh University, and Jane Kirk, the university’s dyslexia study adviser.

In a project set up for the film, Mikey is one of 50 inmates tested for dyslexia - a random sample of offenders sentenced for burglary, car theft, drugs offences and assault. Almost all are being screened for the first time ever.

In the population as a whole, between 4 and 10 per cent of people are affected by the range of learning difficulties classified as dyslexia. But previous research has suggested a higher than average incidence among young male prisoners. An article in The TES Friday magazine (February 19) revealed that one in three prisoners at London’s Pentonville Prison are dyslexic. Before making the programme Gavin Reid and Jane Kirk had anticipated that the proportion at Polmont might be between 15 and 30 per cent.

On Monday night we meet the young offenders as they are being screened.

Mikey took the criminal path after truanting from school. After a series of offences, he was sent down for robbing a garage. He admits he’s still bad at writing and, with other inmates at Polmont, goes to basic skills classes.

As well as Mikey, we meet Thomas - aged 18 and convicted four times already for house burglary. His education seems to have been a write-off. Although he was asked to leave five primary schools for bad behaviour and bullying, his learning difficulties were never examined so his dyslexia went undiscovered.

The camera eavesdrops on the young offenders concentrating fiercely in front of the computer screens. We see lips forming words as the young men do silent reading. In one interview we hear Greece named as the capital of Italy; and one boy cannot repeat to the examiner a simple sequence of numbers.

The results of the screening are dramatic - half of the inmates at Polmont show indicators of dyslexia. Jane Kirk says: “Dyslexia is a continuum of processing difficulties, and 50 per cent of the sample were somewhere on that continuum. Many of them had many of the indicators, and few were borderline. We identified more young dyslexics than we expected. The diagnosis gives them the chance of a new start.”

Some of the young offenders break down in terars when they discover that, while they clearly have specific learning difficulties, they are not “thick”. Several wonder why they could not have taken such a simple test much earlier in their lives.

Dyslexic Criminals ends with a striking image - Mikey, the “hard man” of the primary school playground, is released and his mother meets him outside the prison. He weeps uncontrollably and clings to her. Where will this macho, vulnerable, severely disadvantaged boy go from here?

The film’s clear message is that when schools fail to recognise and help dyslexics, particularly those from socially deprived backgrounds andor dysfunctional families, they may be caught up in a cycle of frustration, truancy and crime, which eventually dumps them in prison.

Before she took the job at Edinburgh University, Jane Kirk was principal teacher of learning support services at North Berwick High School, and had worked in specials schools in Glasgow and Aberdeen. She has seen how undiagnosed dyslexics, coming up from primary school, start avoiding tasks they can’t cope with and become steadily more impertinent, disruptive and destructive. “They are sent out of class, then excluded for a week, then expelled. And that may be when they begin to mix with the local criminal fraternity,” she says.

“Some dyslexic children develop strategies and can coast along in the bottom group. But many want to demonstrate their true ability, and can’t. People don’t realise how emotional a problem it is for them. I constantly feel sorry for them in their frustration.”

The next step for many of these dyslexic outsiders is to muddle their way into prison. How they do this is explained by an inner-London probation officer, Wally Morgan, who has many years’ first-hand experience of criminals and has carried out a major survey of the learning difficulties of 150 adult offenders in London.

“They get dates and days wrong and fail to turn up for important bail appearances in court,” he says. “Addresses can be a problem. So probationers often have difficulty finding the office they are supposed to go to.”

He also explains that when dyslexics are interviewed by the police, their inability to sequence, coupled with poor short-term memory, often leads them to incriminate themselves - even when they are innocent.

Early on in the film, before the researchers start their tests, Les Wiley, Polmont’s head of education, says he expects them to show that the inmates of Polmont are no more dyslexic than the rest of the population.

The governor, Dan Gunn, who allowed the research and filming to take place in his institution, must have been startled by findings so widely at variance with what his head of education expected.

He acknowledges the importance of the issue, but says the entrenched frustration of undiagnosed dyslexics is something that the school environment has to pick up and deal with as early as possible.

After the results of the research became known, the researchers offered to hold a seminar at Polmont to raise awareness of dyslexia, and discuss their findings with the staff. At the seminar, the governor listened, but remained non-committal.

He told the TES that Polmont has, like other prisons, “been trying to prioritise learning and basic skills in the prison service for many years. “We’ve found it difficult. Our aim is to create a learning environment.”

Dan Gunn may well be reflecting some of the general caution in the Scottish prison service over the whole issue of dyslexics in jail. This caution is surprising in view of the available statistical evidence - of which Gavin Reed and Jane Kirk’s report is just a small part.

For instance, a 1995 Swedish study showed that in an Uppsala prison, 39 out of 61 inmates studied (64 per cent) had “reading or writing difficulties”, some caused by dyslexia. Wally Morgan, in his London study, found that, among offenders of average intellectual ability or better, 62 per cent showed signs of dyslexia or some similar learning difficulty.

Lillias Noble is the new full-time education adviser to the Scottish Prison Service. She admits prisoners are likely to have a high incidence of specific learning difficulties. But for her, dyslexia is a “sub-set” within the policy of trying to improve core skills across the board. “We don’t want to start with dyslexia, but we do make available a resource book and teaching and learning materials provided by the Scottish Dyslexia Association, which can be used with prisoners.” But in her recent 10-page internal document, Prisoner Education Policy, the word dyslexia does not appear.

In the England and Wales prison service, the main thrust of education policy is also “to improve prisoners’ basic literacy and numeracy skill”, according to its corporate plan, Reducing Crime. But a Dyslexia Information Pack produced in February 1999 and sent by the prison service to every penal institution in England and Wales, is cautious about how much of it there is in prisons. It says: “Recent research suggests that there may be a higher proportion (than in the general population) who experience dyslexic difficulties.”

To be fair, the document usefully points out the key emotional effects of dyslexia - “feelings of low self-esteem and lack of confidence which sometimes result in negative ways of dealing with new or difficult situations.” And it advocates “accurate screening” as “an essential first step”.

Programmes to help dyslexic inmates operate in Pentonville and other English prisons, but screening is not mandatory.

Now Gavin Reid and Jane Kirk’s study has been sent to the Home Secretary, Jack Straw. Ms Kirk is a passionate advocate of a proper recognition of dyslexia, but she makes a modest proposal to Mr Straw. “Nobody is asking for full learning support for every prisoner, but raising awareness of dyslexia in every prison could be done cheaply and quickly.”

Channel 4 broadcasts three documentaries next week, ‘Dyslexic Genius’ (July 25, 8.30pm) ‘Dyslexic Criminals’ (July 26, 8.30pm) and ‘Dyslexic Children’ (July 29, 8pm)Channel 4 has also published a free dyslexia information pack, consisting of a booklet and cassette. Tel: 0845 6102210