They will be able to choose between grammar schools, totally or partly selective grant-maintained schools, GM comprehensives, council comprehensives with or without “grammar streams”, church schools, independents, specialist schools, or city technology colleges, all with their own entry tests.

The idea is being sold as diversity through deregulation. Critics argue that it sounds more like a recipe for chaos and say that the Government has not indicated how many pupils it envisages should be selected in total across the country.

Legislation is impossible before the next election, but if the Tories win, and GM, specialist and comprehensive schools are able to select 50, 30 and 20 per cent of their pupils respectively, the result looks likely to be an intensification of the present situation, with pockets of the country, particularly large cities and the South-east, operating selection, while rural areas retain the comprehensive system that seems to suit them.

The two types of school most likely to take up the Government’s offer are comprehensives, whether council or GM, whose intake is already threatened by selection in the area, and specialist schools, which are often oversubscribed.

Selection breeds more selection. In areas like Sutton on the outskirts of London, which has 14 secondary schools, half of which are opted-out and operating selection in some form, the pressure would be on the comprehensive heads if more schools started choosing pupils.

“I can see no educational justification for increasing the number of selective places in Sutton, and no educational advantage for this school,” says David Harding of Stanley Park high, a Sutton comprehensive. “But if more schools become selective, or selective schools start selecting more, we’d be in a difficult position. If we selected 20 per cent, it might give us more of a fighting chance, and it might improve the local perception of this school if it had a grammar-school stream - but it would be a pragmatic rather than a principled decision.”

He also says that between 20 and 25 per cent of children are already selected in Sutton, so if this were to increase to 30 or 40 per cent, “it would be pseudo selection” - a fight for the best of the rejects.

At the Beacon GM comprehensive, just over the border in Surrey, headteacher John Darker is in a similar position. “There is already a creaming effect due to the large number of selective schools in this area, and now two more are applying. If they do, we’d have to consider 50 per cent selection, but it would be with regret.” He worries about pupils with special needs in an increasingly selective environment. “We’ve got 40 children with statements already, while the selective schools average about 10.”

In inner-London Lambeth, where half the secondaries already select, the position is complicated by competition from neighbouring Wandsworth.

Dunraven GM school’s request to select half its pupils, turned down a year ago, is currently being reconsidered by the Secretary of State. The school is competing with three city technology colleges selecting to create a balanced intake, a technology college, Graveney GM school (selecting 50 per cent) Burntwood GM (30 per cent), a magnet school, independents and several church schools selecting by faith. It is not difficult to see how the comprehensive commitment may buckle.

By contrast, Robert Dupey, head of Ecclesbourne GM school in Duffield, Derbyshire, said selection was unlikely to become an issue. “We wouldn’t gain anything from it. All the schools round here are comprehensive and of similar size - parents choose on the basis of distinctive ethos.”

Increasing selection in the Government’s unplanned way would result in it becoming an urban answer to an urban problem, he said. “It’s a domino effect. Comprehensives will hold the line up to a point, but if one or two break ranks, the others have to think in terms of self-preservation.”

Specialist schools appear to be here to stay - Labour’s attitude to them has become progressively warmer. There are now 127 technology colleges, 20 language colleges, plus the original 15 CTCs. The White Paper now proposes specialist sports and arts schools.

Some CTCs argue that they are best models of comprehensive education because they select across the whole ability band, then select for aptitude from each band - thus eliminating the “selection by house price” problem which makes comprehensive education such a battleground in places like inner London.

The situation with the other specialist schools is more complex. Originally, specialist status was only available for GM schools, so these will have their own criteria. However, many of the LEA comprehensives which subsequently won technology or language status did so in order to give all pupil access to the benefits the status brings, and insist they have no intention of selecting for aptitude.