Amazon has agreed to channel funds to a controversial drug rehabilitation charity linked to the Church of Scientology, the Guardian has learned.

The web giant will make donations to Narconon – which runs programmes for drug addicts based on the teachings of the Scientology founder, L Ron Hubbard – when supporters buy products through the site, with shoppers able to pledge 0.5% of purchases to selected charities under Amazon’s “Smile” feature.

Narconon, funded via the Church of Scientology, whose celebrity followers include Tom Cruise and John Travolta, uses cocktails of vitamins, exercise and lengthy daily sauna sessions as part of its treatment programme. Experts have warned the charity’s methods have no scientific basis and its link to Scientology has prompted criticism that it is a front used to convert people to the religion, which some former devotees have labelled a cult.

Tens of thousands of children as young as 10 have been given talks by Narconon at schools across the UK, of which many were apparently unaware of the link to Scientology, leading to complaints from parents.

The Guardian discovered that Amazon US allows shoppers to donate funds to more than a dozen Narconon-related charities, including its international branch based in Clearwater, Florida, near Scientology’s “spiritual headquarters”.

Meanwhile, Amazon’s UK website lets consumers donate to Narconon’s branch in Twickenham, south-west London. The organisation claims to have reached tens of thousands of pupils across the south and Midlands with anti-drugs talks in schools last year. The charity’s Twickenham branch accounts on Companies House state: “In 2018 a significant legacy donation has allowed us to increase our delivery considerably, reaching 22,261 students and teachers in the south and Midlands with our interactive talk The Truth About Drugs and we continue to take on an expanding number of schools. It has also allowed us to invest in audio-visual aids to our talks. The donations that we receive are utilised extremely efficiently, with a cost of approximately £1.30 to reach each child or teacher with our talk.”

Prof David Nutt, who formerly chaired the government’s Advisory Council on the Misuse of Drugs, said Narconon’s claim about telling “the truth about drugs” in its talk was not correct. He said: “Though I can’t see the school teaching material on the web – based on the info re Narconon I suspect that it won’t be truly scientifically or evidence based. Sadly we have known for years that Scientology is the main provider of ‘teaching’ materials on addiction to schools, as the UK government doesn’t fund any alternative sources.

“The Narconon treatment invokes concepts of residual drug in body and brain which have no scientific validity. Moreover, they do not provide any data on success rates – just a few testimonials.”

Scientology, founded in 1954 by science fiction writer Hubbard, has proved hugely controversial, with critics claiming it is a brainwashing cult that harasses followers who quit the church. The church denies the allegations. Ex-Scientologists say the religion’s doctrine centres on the belief that 75m years ago Xenu, an alien from space, massacred alien life forms with hydrogen bombs in volcanoes, with their souls causing humanity’s evils.

In 2013, Scientology was officially recognised as a religion in the UK in a ruling by the supreme court. But many other countries still refuse to follow suit.

Narconon, which is a registered charity in the UK, is coordinated by the Association for Better Living and Education (Able), which is funded via the Church of Scientology and its followers. The charity says it operates in more than 20 nations running treatment centres, including one in Heathfield, East Sussex.

Amazon was unable to say how much money it has channelled to all of the registered Narconon charities – although it is understood no funds have yet been passed to the UK-based branch – but it opens up a potentially lucrative new revenue stream. As of July 2019, AmazonSmile has generated more than £110m worldwide for charities and over £1.9m in the UK. An Amazon spokesman said: “The Charity Commission is the official charity regulator in England and Wales. If an organisation no longer has charitable status – for whatever reason – and has been removed from the commission’s register, we will also remove them from the AmazonSmile programme.”

Noel Nile, the president of Narconon UK, said the organisation received donations from a variety of sources and described Amazon’s Smile programme as an “excellent fund-giving initiative”. “Narconon educators have given lectures to 27,000 pupils and teachers in the past year, empowering the pupils with the knowledge of the dangers of drugs so they can make right choices. The need for effective drug prevention has never been higher,” he said.

Nile highlighted a Narconon-funded academic paper published in the Journal of International Medical Research in 2018 that studied the safety and preliminary health benefits of the organisation’s drug treatment programme on 109 participants. The paper found improvements in mental and physical scores of participants of the sauna detoxification programme, concluding that “broader investigation of this sauna-based treatment regimen is warranted”. Prof Nutt pointed out that the paper looked at “safety and tolerability … not efficacy”.