A Swedish childcare "expert" who was called to brief MPs last month on the dangers of subsidised daycare has been attacked as "unscientific" and "unqualified" by the author of the main study on which he drew.

Jonas Himmelstrand, the keynote speaker at a House of Commons event organised by the campaign group Mothers at Home Matter, linked near-universal pre-school daycare in his country to an alarming decline in adolescents' mental health and educational achievement, as well as to rising youth suicides. "This is a dream which failed, which any country attempting to emulate should be warned about," he said.

After the talk, David Davis, a former Conservative party leadership candidate, commended Himmelstrand for his "startling figures", which he said demonstrated that "separating children from their mothers at an early age and putting them into care while the mother returns to work can have damaging consequences". However, Dr Sven Bremberg, a researcher at Sweden's Karolinska Institute who led the 2006 inquiry into youth mental health cited by Himmelstrand, said his study had ruled out daycare as a cause. "There is no substance whatsoever behind Himmelstrand's statement that a decline of mental health in young people in Sweden is related to daycare. That was one of the points we specifically investigated," he said. Bremberg said that Himmelstrand should not be taken seriously by British MPs. "Himmelstrand does not have scientific qualifications as far as I know. By misquoting, he is handling arguments in a very unscientific way."

The Mothers at Home Matter event was hosted in the Commons by Claire Perry, a Conservative MP who is David Cameron's official adviser on parenting and childhood. It was attended by Iain Duncan Smith, the work and pensions secretary. The group, formerly known as Full Time Mothers, gained prominence earlier this year after the government announced measures aimed at helping mothers return to work, including shared parental leave and, last month, a new tax break on childcare worth up to £1,200 per child per year.

The government's reforms reflect the influence of Nordic family policy, which combines generous shared parental leave with heavily subsidised daycare to keep mothers in the workforce. In Sweden, 83% of one-to-five-year-olds spend time in daycare, with the cost to parents capped in Stockholm at around £130 a month for the first child, £85 for the second and £42 for a third.

Himmelstrand's talk received enthusiastic coverage in the Daily Mail and Daily Telegraph, which referred to him respectively as a "researcher" and "psychologist". Lynne Burnham, the secretary of Mothers at Home Matter, told the Observer that Himmelstrand's research was "all based on proper scientific figures". She said: "He works quite closely with an American professor and sociologist. I can certainly send you some of his research papers."

When contacted by the Observer, however, Himmelstrand said that he had been "self-taught", although his late father was an internationally known sociologist. "I cannot say I have an academic degree, and I have never claimed to have one," he said. "Some British media have mistakenly written that I am a sociologist. This is not correct." In the introduction to his House of Commons talk, he said that he was the founder of the Mireja Institute and a "faculty member" of the Neufeld Institute, founded by Canadian psychologist Dr Gordon Neufeld. Last week, however, he conceded that Mireja was a "one-man outfit". The Neufeld Institute says on its website that it invites people to become "faculty members" if they complete an advanced course in home-schooling and a two-year internship at its "virtual campus", at a cost of more than £8,000.

Himmelstrand blamed Bremberg's criticisms on "a misunderstanding", saying he had only cited the study to support his claim of deteriorating youth mental health in Sweden. The link to daycare had come from other studies, particularly a 2001 study by the National Institute of Child Health and Human Development in the US. "I am convinced that I have a strong argument, strong enough to question whether a system like that in Sweden should be adopted without further study by other countries," he said.

HeHimmelstrand conceded that there had been no study since the 1980s to investigate the links between high enrolment in daycare in Sweden and mental health in later life. "The Swedish government shows no signs of wanting to study the effects of daycare," he said. "It is like a totalitarian system defending its ideology at any price. A study showing that the Swedish daycare system is not in all children's best interest would shake the Swedish political system."

He argued that this also meant that Bremberg, whom he described as "on the extreme pro-daycare side in Sweden", was overstating his case. "Dr Bremberg is making too strong a claim in saying: 'There is no substance whatsoever … that a decline of mental health in young people in Sweden is related to daycare.' No one can claim this either way scientifically. There are simply too many factors."

When challenged on Himmelstrand's qualifications to brief MPs, Burnham noted that he had given speeches on daycare in other countries. "He travels the world speaking on these issues, so I guess there must be some credibility to these figures," she said. "It's not just Himmelstrand who's been saying this; there are other people saying the same thing."

As well as Bremberg's study, Himmelstrand's cited research by a Swedish psychologist, Magnus Kihlbom, which he said demonstrated that a decline in the quality of Swedish daycare meant that it was now actively harming many children. When contacted, Kihlbom dismissed Himmelstrand as "probably a conservative". "I don't think it's a question of either/or," he said. "Even for very small children, daycare of good quality with reliable relationships between the carer and the small child is good for most children."

A review of the evidence on daycare by the Institute for Public Policy Research, to be published next month, has concluded that the overall impact on child development is beneficial. "There's now a fairly strong body of evidence that high-quality care has a positive effect on both cognitive development, and also emotional, social and behavioural development," said Imogen Parker, the author of the paper. "There are some studies that found that, for the under-threes, there might be a trade-off between positive cognitive effects and negative behavioural effects, but where that is the case these negative effects are short-lived and not particularly pronounced."

Himmelstrand, who is a fervent advocate of home schooling, has moved his family to Åland, a Finnish island a three-hour ferry ride from Stockholm, because he fears that the "trigger-happy" Swedish social services might take his children into care. He supports himself primarily through his work as a consultant promoting the "mentoring" ideas of Mike Pegg, a British management writer, and doing presentations on Neufeld's work. He denies being a political conservative, but is a regular speaker at the Stockholm Freedomfest, a Swedish offshoot of a gathering for radical libertarians set up by Mark Skousen, a devout Mormon free-market economist.

Perry and Davis both declined to comment for this article.