Analysis of those free schools already approved by the Education Secretary, Michael Gove, reveals that many have been set up in areas where existing schools already have surplus places.
Their arrival has caused a loss of pupils for existing comprehensives – threatening their viability, says the report. In one school – an academy highly rated by Ofsted, the education standards watchdog – the headteacher estimated he will lose £1m a year as a result of a new free school being set up.
So far, 24 free schools have been opened by the Government – run by parents, teachers and faith groups. A further 70 will open in the next 12 months.
Kevin Courtney, the deputy general secretary of the National Union of Teachers which published the survey, said the free-school policy was "a waste of taxpayers' money". "It is damaging children's education," he added.
The threat to neighbouring schools comes at a time when there is real pressure to open more primary schools because pupil numbers are rising by 450,000 as a result of an increase in the birth rate. However, many of the free schools are secondary schools, the report observes.
Cases cited in the report include the Beccles Free School in Suffolk – which, its opponents argue, could jeopardise the future of the highly rated Sir John Leman Academy. Jeremy Rowe, the academy's headteacher, has described the new free school as a "disaster", adding: "You can't invent children: there are a given number who go to school in Beccles." He estimates that the new school, supported by his local Conservative MP Peter Aldous, could cost the academy £1m.
A Bristol free school is being set up in an area of the city where four new schools have been built, and which already have 300 surplus places between them. In September last year, the free school was well below its target figure of recruiting 150 pupils – taking in just 70.
Becket Keys Church of England School in Brentwood, Essex, is being opened on the site of a secondary school closed because of a fall in pupil numbers. Neighbouring schools already says their rolls are down this year.
In Chorley, Lancashire, a free school with provision for 500 children will open in September despite the fact there are already 400 surplus secondary places in the town.
"It is not just the usual suspects that are against this," said Mr Courtney.
Under the legislation setting up free schools, Mr Gove is required to carry out an impact assessment of the effect any new school will have on the neighbourhood. However, a Freedom of Information request from the union to see his assessments met with a refusal on the grounds that he is allowed to withhold the information if it is to help him make a political decision. The NUT is now complaining to the Information Commissioner, claiming that it is in the public interest to publish the assessments.
Today's report says: "There is evidence that the views of local authorities are currently being ignored where they have raised concerns about the negative impact of a new school. This cannot be in the interests of pupils, parents or the taxpayer."
A spokeswoman for the Department for Education said: "Many of the first free schools were set up by talented heads and teachers with years of experience in state schools. These professionals listened to what parents had to say and responded with more local choice for children. As a result, the vast majority are oversubscribed.
"It is disappointing that the work of these teachers is being overlooked by the NUT."
Meanwhile, Chris Keates, general secretary of the National Association of Schoolmasters Union of Women Teachers, claimed Mr Gove was "intent on recreating the world of the 1950s grammar schools".
In her speech to her conference in Birmingham, she said that was "a time when élite universities had control of school examinations which were essentially entrance examinations for Oxbridge".
"This is not an education service fit for the 21st century – these are regressive, elitist education policies designed to set up a quasi-independent school sector funded by the state," she added.
CLASS WAR: PILFERING PUPILS
The Bristol Free School has created empty places in four surrounding schools, including Henbury School, an academy in north Bristol.
The establishment of Lancashire's Chorley Career and Sixth-Form Academy will directly affect the nearby Runshaw and Preston colleges.
Derby Pride Academy – an alternative provision free school – will threaten the viability of Kingsmead Pupil Referral Unit in Derby.
Becket Keys Church of England School in Brentwood, Essex, is to be given free-school status despite neighbouring Shenfield High and Brentwood County High reporting that their admissions are down.
Sir John Leman High School in Suffolk estimates it will lose £1m a year as a result of the establishment of Beccles Free School.
Sandymoor School, a 900-place free secondary in Runcorn, Cheshire, could put two of the area's other secondary schools at risk. They already operate below full capacity.
Of the 60 children enrolled at Canary Wharf College – a free infants' school in London's Docklands – 16 transferred from a neighbouring school.
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