Thousands of prisoners are claimed to have links to the cult-style religion founded by sci-fi writer L Ron Hubbard, which counts Hollywood star Tom Cruise and John Travolta among its converts.
An arm of the religion called Criminon says it now has followers in all of the 139 prisons in England and Wales and many of the 16 prisons in Scotland.
However Ministry of Justice figures show just three inmates are scientologists, compared with 23,000 Church of England members, 14,000 Catholics, 366 Pagans and 340 Rastafarians.
A spokesman for Criminon said that it had delivered its crime and drug rehabilitation programme to every single prison in the UK.
He said: "Criminon UK has delivered the CRIMINON Programme in a total of 140 prisons."
It's website then lists every single prison in England and Wales and boasts that its anti-drug rehabilitation programme - which it touts around prisons - aims to change the behaviour of inmates.
It states: "Criminon UK provides crime prevention and rehabilitation programmes to people in need.
"It also delivers drug rehabilitation programmes to offenders. It is a registered charity and the programmes are available to anyone regardless of race, religion, sex, age, disability or offence committed.
"Criminon organisations worldwide provide the programme using courses that address some of the key factors that are known to cause criminality; such as lack of self respect, illiteracy and a lack of moral values."
In a Freedom of Information request, The Ministry of Justice admitted that Criminon tried to 'recruit prisoners' by writing to them in jail and encouraging them to sign up to the programme.
The MoJ states:"Criminon is a secular arm of the Church of Scientology. It is a Scientology-based course which aims to reduce re-offending, with particular emphasis on drug misuse.
"Whilst Criminon claim to have been providing a programme to prisoners in England and Wales, the National Offenders Management Service (NOMS) do not endorse or fund Criminon.
"NOMS is aware that Criminon periodically attempt to recruit prisoners and have offered prisons courses, sometimes free of charge.
"Prison staff have been provided with guidance stressing that interventions offered in prisons must be compatible with the existing treatment strategy and fit for purpose.
"NOMS is aware of a number of cases where prisoners have engaged in correspondence with Criminon.
"Rules concerning prisoners' access to letters contain the presumption that correspondence will not generally be restricted or stopped unless the restriction is a proportionate response (i.e. a threat to national security, prevention of crime).
"Legal advice is that letters from Criminon do fall into this category and therefore should not be withheld from the prisoner to whom they are addressed.
"Prison staff have been advised to guide any prisoners who have been contacted by Criminon toward a Counselling, Assessment, Referral, Advice and Throughcare referral.
"This will provide an opportunity for the prisoner to engage with the validated framework for drug treatment and support."
