Parent groups, businesses and charities would be expected to pay millions for school buildings, with no hope of a return, under Conservative and Liberal Democrat ideas to diversify the state school system.

This, together with their refusal to allow school operators to make a profit, is likely to jeopardise their plans for a Scandinavian-style “free schools” system.

Like Labour, both opposition parties are now wedded to the notion that greater choice and diversity among state-funded schools is the best way to raise standards.

That belief has been the rationale behind the Government’s promotion of specialist schools and latterly academies and trust schools.

But the Opposition believe you can go further still. The Tories and Lib Dems want to encourage many more outside groups, parents, charities and companies to set up their own schools offering free state-funded education as alternatives to existing maintained schools.

Both parties have been inspired by Sweden, where a 1992 decision to allow independent schools to receive the same Government funding per pupil as state schools led to an explosion of “free schools” that do not charge fees but are outside the state system.

The Lib Dems even used the same name for their “free schools” policy. The idea, in the words of their leader, Nick Clegg, is to “allow for a genuine blossoming of variety in the schools system.”

Michael Gove, the Conservative shadow schools secretary, said last week that encouraging new independent state-funded schools in England, even when there are surplus places, would replicate the Swedish experience, where 15 per cent of pupils go to free schools.

“If we had Swedish-style reforms, there is every reason to believe that we would have up to 3,000 new schools,” said Mr Gove. But is there? Both parties’ policies have two major differences with the Swedish model.

Firstly, they say operators of these new free schools should not be allowed to make a profit, something that is allowed in Sweden.

Secondly, they say it will, to a large degree, be left up to the providers to buy or rent the builings needed to house these schools.

“We cannot run our schools system where you are simply giving a blank cheque for anyone who wants to open a school,” David Laws, the Lib Dem’s schools spokesman told The TES.

“That would be potty. Within five minutes the Government capital budget would be overloaded. If the local authority is not actually inviting tenders for a new school, then the provider would have to find the capital side themselves. They would have to bear the capital risks in providing that facility.”

The word “risks” makes it sound like an investment with a potential financial return. But if the providers are not allowed to make a profit, that will not happen. Instead, the money they pay for a school building will effectively be a donation to the state-funded education system.

The Conservative Party has said that assuming current funding levels continue, it will provide pound;4.5 billion over nine years to build new privately-operated schools.

The money would come from redirecting 15 per cent of the Building Schools for the Future budget, which the Tories argue could be spent much more efficiently without the bureaucracy involved in such a big scheme.

But even then it would only work out at pound;1.5m for each of their projected 3,000 schools, a fraction of the average cost of a new primary, let alone a secondary.

So what about the rest? Mr Gove notes that in Sweden, school operators often rent or lease buildings rather than buy them and that the same could happen here.

That would, of course, still cost money. But Mr Gove’s basic position is that if the system can work there, where average per pupil funding is significantly lower, then it will also work in England.

But TES enquiries suggest the Conservatives have missed an essential element of the system that has inspired their policy - the fact that Swedish free school providers receive an extra 15-20 per cent per pupil funding for their capital costs.

Mr Gove denies this is extra money, insisting that all Swedish free schools receive exactly the same money as their state counterparts, even though the state schools don’t need new buildings.

“I didn’t find any free school supplier that said, `we are incredibly lucky and the local authority provides us with more money than they spend on their schools’,” he said.

But Kunskapsskolan, the company running some of the free schools that the Conservatives have been taking journalists to visit in Sweden, begs to differ.

Anders Hultin, a founder of the company and its UK managing director, said that some Swedish local authorities did pay free schools more per pupil in recognition of the fact that they had to buy or rent buildings, unlike existing state schools where buildings were already council owned.

Other Swedish authorities opted for a “purer” system, which meant that conventional state schools were now expected to pay rent to the council for buildings.

This placed the conventional schools on a level playing field with the free schools, with all receiving the extra capital funding.

But in both cases it has been recognised that free school operators cannot be expected to find the cost of buildings from their own pockets - something that neither Conservatives nor Liberal Democrats seem prepared to accept.

Mr Hultin has another problem with their approach: his company is planning to sponsor four or five academies but will not do anything on a larger scale while it is not allowed to make a profit.

“Operators make an investment in schools and they expect a return on their investment,” he said.