An alternative healer who promoted a “slapping therapy” taken up by millions of people across the world has been found guilty of the gross negligence manslaughter of a British woman who died at one of his workshops.

Danielle Carr-Gomm, 71, who had type 1 diabetes, fell fatally ill in 2016 after she stopped taking her insulin and fasted during a paida lajin therapy retreat run by Hongchi Xiao at a country house in Wiltshire.

The prosecution claimed Xiao, 61, who is addressed as “master” by his followers, was in charge of the workshop and had a duty of care towards Carr-Gomm.

They said he was grossly negligent by failing to take reasonable steps to encourage her to take insulin and to summon medical help when it was clearly required. When she became seriously ill, crying in pain and weakening, Xiao blamed her decline on a “healing crisis”.

After the verdict, Carr-Gomm’s son said on behalf of the family that Xiao was a “complete fraud”.

“While we cannot bring our mother back, we hope this case at least highlights the dangers of pursuing unregulated alternative therapies without proper research,” he said.

“Our mother’s motivation was to live, and had she not been deceived by this man, whom she trusted to care for her, she would not have knowingly risked her life in such a manner.”

The prosecution said Xiao should have been fully aware of the danger Carr-Gomm was in because the year before a six-year-old boy with type 1 diabetes had died at a workshop he ran in Australia after Xiao had told his mother to stop giving him insulin. Xiao was convicted of gross negligence manslaughter over the boy’s death in 2019 and jailed.

During the trial at Winchester crown court, Xiao described how he had learned paida lajin from kung fu masters and hermits in the mountains of China and had spread the “forgotten” method to “millions” of people around the world.

Xiao, who was born in China, said he had quit a lucrative career in finance to focus on paida lajin and was not in it to make money. He said the technique, which involves slapping and stretching, was easy to learn, helped tackle every disease known to humans, and reduced the need for patients to take “western” medicine with “poisonous” side-effects.

Xiao said he was not a medical doctor and it was up to participants in his workshops to continue to take the conventional medication they needed. He said Carr-Gomm, from East Sussex, was stubborn and had chosen not to take her medicine or listen to his advice. He said: “I’m not her protector. I was only her teacher.”

Xiao said the deaths of the boy in Australia and Carr-Gomm had led to paida lajin being “demonised” and he suggested it had deliberately been discredited by “western doctors” and alternative practitioners because it put them out of work.

The trial heard that Carr-Gomm, who had a longstanding interest in alternative medicine, had been keen to reduce or stop her insulin injections and considered Xiao a “messenger sent by God” to bring about a revolution in medicine. Family and friends of Carr-Gomm said she had turned to alternative therapies because she was afraid of needles and was a vegetarian. They told the Guardian they were shocked to hear during the trial how much she had suffered.

Her ex-husband, Philip Carr-Gomm, a psychotherapist and writer, said: “None of us knew the suffering she went through at the end. I thought she had just gone to sleep and hadn’t woken up.”

He said their younger son had dropped her off at the workshop at Cleeve House in Wiltshire. “The next thing police were turning up at his flat to tell him what had happened.”

Philip Carr-Gomm said Xiao should have known the danger she was in, given the death of the boy in Australia. “You would think any sane, responsible person would be aware of that risk to start with, but if there was an awful situation like that, you wouldn’t repeat it.”

Xiao will be sentenced on 1 October.