City academies - a new type of school about to come into service - could deprive neighbouring schools of more able pupils, say head teachers.

The problem with city academies is that they are state-funded independent schools

John Dunford, Secondary Heads Association

The Secondary Heads Association has warned that these flagship schools could put other local schools at an unfair disadvantage, drawing in more able pupils.

City academies, the first of which are to be opened this week, will receive start-up funds from private sponsors while the basic running costs are supported by the state.

They are intended to provide centres of educational excellence in deprived, urban areas - and will be allowed a greater degree of flexibility over the curriculum and timetable.

'Cuckoo in the nest'

But the union's general secretary, John Dunford, warned that the new schools could be "cuckoos in the nest", distorting the local education system.

"The problem with city academies is that they are state-funded independent schools," said Mr Dunford.

Although largely funded by taxpayers, the "whole constitution of the school is as an independent school", he said.

And he warned that this could mean city academies competing rather than collaborating with local schools.

City academies - the first of which will open in Middlesbrough and Bexley, south-east London - are intended to be state of the art, innovative schools.

'Diversity'

Private sponsors will provide a fifth of start-up costs, with the government hoping to involve local businesses and community organisations.

There are also plans for academies in Bradford, Bristol, Leeds, Manchester, Nottingham, Northampton, Sandwell, Liverpool and Walsall,

In London, there will be city academies in Barnet, Brent, Ealing, Hackney, Haringey, Hillingdon, Lambeth and Southwark.

The Department for Education said that the new type of school would be "sharing their facilities and expertise with other schools and the wider community, contributing to raising standards across the whole area.

"Diversity in school provision will help raise standards and aspirations for the whole community of schools across the board."