Michael Gove's flagship free-schools policy is in "disarray", government critics claimed last week, after it was revealed that just half of the schools due to open this September had secured a site.
The education secretary announced in October that 79 of the state-funded independent schools had been approved to open at the beginning of the next academic year, but doubts are now being expressed over how many will be ready in time.
Responding to a parliamentary question put forward by shadow education secretary Stephen Twigg at the request of TES, schools minister Nick Gibb admitted that only "around half" of the free schools had found a suitable site.
Finding premises is proving particularly difficult in London and the south-east, where buildings and land are expensive and hard to come by.
According to the New Schools Network (NSN), a charity that works with free-school applicants, the problem has forced "a number" of free-school groups to postpone opening until next year.
Natalie Evans, NSN's chief operating officer, said: "This is something the government really needs to think about. Finding premises is extremely difficult, and is one of the biggest frustrations and a real headache for groups."
Last year, just 24 free schools opened, but the number of applications has grown steadily into the hundreds. Ms Evans has questioned whether the newly created Education Funding Agency (EFA) can cope with the demand.
One free-school group that has been forced to postpone opening until next year is the Compass Schools Trust, which was given the green light last year to set up a secondary in Southwark, south London.
A spokesperson for the trust said: "Finding a site has been our main issue and has meant that 100 local children, currently in Year 6, will miss out on a start to secondary education that they deserve and that their parents want for them."
Louise Buckley, a governor at the Greenwich Free School in south-east London - one of the schools that has found suitable premises in time for the next academic year - called on the government to relax some of the rules that prevent groups from speaking to the owners of buildings and land earlier in the process.
"You aren't allowed to enter into a conversation with the owner of a site until after you have been approved. It means that you may have found a site but it might not be suitable, and you have to start from scratch again," she added.
A spokesperson for the Department for Education said: "Over half of the free schools due to open in September 2012 have now confirmed a site, and we are in the middle of negotiations on preferred sites for the large majority of the other projects."
Mr Twigg said: "The government's approach to school buildings is chaotic. First, the government cut the education building budget by nearly two- thirds - twice the average of other departments. Second, they have delayed their own so-called priority building programme three times. And now their free schools policy is floundering."
Not so free schools
More than pound;330 million has been spent on the government's free schools and academies programmes since the coalition came to power, figures released by the NUT show.
The teaching union said that it had tracked pound;337.2 million in payments supporting the free schools and academies programmes since May 2010.
The union also revealed that 126 full-time equivalent staff at the Department for Education are working on the free-schools programme, despite just 24 being open and only another 79 being approved to open this year.
"Free schools are absorbing an increasing proportion of DfE staff resources at a time when the department as a whole is shrinking," said NUT general secretary Christine Blower.