Swedish Education Minister Jan Bjorklund admitted that his government should have renationalised the country's failing privatised schools seven years ago.

State broadcaster Sveriges Television published figures on Monday showing that 61 per cent of Swedes thought the government should take over, while only 12 per cent disagreed.

Two decades into a controversial free-market experiment about a quarter of Sweden's secondary school students now attend privately run schools.

And nearly half of them study at schools fully or partly owned by private equity firms.

The collapse of JB Education earlier this year, a firm owned by Danish private equity firm Axcel, cost almost 1,000 staff their jobs and left more than a billion kronor (£92 million) of debt to banks and suppliers, as well as abandoning 11,000 students.

With elections next year, politicians of all stripes are questioning the role of such firms, which are accused of putting profits first with practices like performance-based bonuses to staff and advertising in the capital Stockholm's underground system.

"I think we have had too much blind faith that more private schools would guarantee greater educational quality," said parliamentary education committee head and education spokesman for the ruling Moderate party Tomas Tobe.

The opposition Green Party, which like the Moderates was a long-time supporter of privately run schools, issued a public apology in a Swedish paper last month saying: "forgive us, our policy led our schools astray."

Last week's international Pisa education rankings saw Sweden drop below the average for maths, reading and natural sciences across the Organisation for Economic Co-operation and Development.

The revelation has left many keen to reintroduce the nationalised schooling system that was abolished in 1991.

The Pisa results found that Sweden had fallen faster and harder than all other 32 countries measured and performed particularly badly in mathematics over a 10-year period.

The report prompted scathing criticism from Swedish teachers' union Lararforbundet.

"We're losing ground on all fronts and find ourselves in a very precarious position," Lararforbundet president Eva-Lis Siren said.

"A lack of equality is the price Sweden has paid as a result of free choice.

"It's been easier to start an independent school than set up a hot-dog stand."