Thirteen secondaries in Bromley, south London, have joined forces to set admission tests on the same day in November.

They are making use of Education and Employment Secretary Gillian Shephard’s decision earlier this year to raise the number of pupils who can be chosen on academic ability from 10 per cent to 15 per cent of school rolls.

But headteachers say they have been forced into the move by another school in the borough, Hayes school, which has applied for permission to raise its academic intake to 25 per cent.

Under the plan for borough-wide tests, the headteachers will tell parents their children can only apply to one school.

They say the move is aimed at protecting the schools from being deprived of able pupils by Hayes school if it gets the go-ahead to increase selection.

But Tory councillors are unanimously opposed both to the move by Hayes school and the selection plan by the other 13 schools, 12 of which are grant-maintained.

They say the borough already has two grammar schools - one, St Olave’s, recently hit the headlines when Labour front-bencher Harriet Harman’s son was admitted - and the new moves will add to the problem of children from outside the borough taking precedence over local residents.

Brian Humphrys, Tory chairman of Bromley council’s education committee, said: “We already have diversity. What this further change will do is to disenfranchise local parents who will have even more difficulty getting their children into Bromley schools.”

Several Bromley schools already specialise in drama, dance, music, sport or technology. But the authority has long been angry that under the so-called Greenwich judgment, about 700 of the 3,000 pupils admitted each September come from outside the borough.

Robert Dilley, head of Coopers school, a 1,400-pupil comprehensive in Chislehurst and one of the 13 in the consortium, said: “We’ve come together to work in this way because once it was clear that each school was going to adopt the 15 per cent criterion, we wanted to make sure that there was a co-ordinated approach.

“We’ve agreed to hold tests on the same day to try and make sure children aren’t touted round from school to school. But 85 per cent of children will still be admitted according to how near to the school they live.

“It’s not an attempt to bring back the 11-plus when all primary school children took a test and were divided into sheep and goats.

“All the schools will be setting tests, so in a sense it doesn’t change anything and is actually an attempt to keep things as they are.”