The Today Programme has discovered that the government has already started promising or even handing out money to 35 Free Schools.
Francis Gilbert, a teacher opposed to the idea, told Today presenter Sarah Montague that there was a "a massive lack of transparency" in the funding of the schools.
It was "unfair" he said, when other state schools were having their funding "slashed", for Free Schools to have their building projects funded.
"At the moment it looks like these free schools are going to be very expensive schools indeed," he said.
But journalist Toby Young, who is setting up a Free School in west London, said that the majority of free schools would be set up in refurbished existing buildings.
"We know that that's a much cheaper way of providing much needed school places," he said.
While deregulating free schools so that private companies could profit from setting them up could save even more money, he said, Free Schools in old buildings were far more cost effective than building new schools.
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