A leading academic authority on school admissions has delivered a stark warning to the Government that expanding the academies programme and creating free schools will drive up unfair selection.
Education Secretary Michael Gove has made such expansion his key priority since being appointed, highlighting the additional autonomy over areas such as admissions policy as a crucial selling point.
But speaking to The TES, Anne West (pictured), director of the Education Research Group at the London School of Economics, said there was "cause for concern" when it came to the expansion of academies and free schools.
The problem would be exacerbated by factors such as league tables, leading to these "independent" schools wanting to "take on" more able students, she added.
"The potential is certainly there (for an increase in social selection)," Professor West said. "It doesn't have to be like this. If everybody is playing by the rules they could carry out their own admissions. But schools are in competition with one another and because of this competitive environment they don't want to take on kids that are harder to teach."
She added: "There are undoubtedly tensions in policy between equality and freedom. On the one hand you have the drive to increase social mobility, and on the other you have the autonomy of schools - and they don't necessarily fit together."
Professor West co-authored a research document commissioned by the previous government, which was released last week, calling for an external body to administer admissions in order to increase transparency and restore faith to the admissions process.
"Previous studies have shown that schools that are their own admission authority are more likely to have admissions criteria that enable schools to be unfairly selective in their intakes. There is therefore a case for moving admission powers away from individual schools and putting them in the hands of an independent body that administers admissions across an area and ideally sets admissions criteria that are consistent across all schools," the report said.
Mary Bousted, general secretary of the Association of Teachers and Lecturers, said Professor West's comments echoed her own fears over policing of the admissions code.
"I have asked Michael Gove time and time again: 'Who will enforce the admissions code?' Because if we do not have someone to enforce it, the admissions code is toothless," Dr Bousted said.
"The pupil premium is unlikely to be incentive enough to make schools take pupils from more disadvantaged backgrounds," she added.
The government report comes just a month after similar research was published by children's charity Barnardo's, which reached the same conclusion. The report said schools that have control over their own admissions are more likely to be socially selective than maintained schools.
But James Groves, head of the education unit at Policy Exchange, said a pupil premium would combat the notion that academies could skew admissions in favour of any one socio-economic group, adding that academies have always been able to select 10 per cent of their pupils on aptitude.
"It has been the case for the last seven or eight years and so it will be going forward. It is clearly a part of the programme that academies should have autonomy over their admissions," Mr Groves said. "Obviously, the Government does need to be careful and monitor admissions. But I would certainly not advocate a central body to oversee admissions."
A DfE spokesman said: "All academies must comply with the same statutory national admissions code as any state school - and the Government has been clear that it will be simplifying the code to make it fairer and clearer for parents and to reduce bureaucracy on schools.
"The National Audit Office has looked at all academies and found that the creation of academies has no negative impact on neighbouring schools intakes, backing up what PricewaterhouseCoopers also independently reported in 2008."