The heads say the discrepancy, which has been thrown up by the complex workings of the Common Funding Formula, could scupper the hitherto good relations between local authority and GM schools in the borough. "If this continues, I can't believe the authority would retain its secondary schools for long," said one head.
Irene Byard, head of Enfield County Girls' School, pointed out that a boys' GM school, Enfield Grammar, was "just across the alley". "I've just had to write to parents explaining why their sons are going to get more than their daughters," she told The TES.
The Labour-controlled council, meanwhile, has condemned the allocation for GM schools as "unfair, divisive and inequitable" - but is obliged to implement it. The council is now combing its budget to see if it can find the estimated Pounds 1.66 million needed to bring the budgets of its 12 local authority secondaries up to the level of the five GM schools.
The difference results from the new way in which the Funding Agency for Schools (FAS) calculates the sum GM schools in an area should receive. Under the Common Funding Formula, this is based on the standard spending assessment for schools in each local authority, minus a sum to cover services like special needs still provided by the council (the so-called "top slice").
From April, the way of calculating the "top slice" has been changed, notably by basing the sum for special needs on national unit costs rather than local figures. Since Enfield spends well above average on pupils with special needs, its "top slice" has accordingly been reduced from 17 to 13 per cent of the schools budget and GM schools allocated their share of a larger total. This will give the borough's five GM schools an extra Pounds 486,000 next year.
Achilleas Georgiu, the council's chair of education, said it was "illogical and ridiculous" to base local assessments on national averages. The council points out that it faces high and growing demands on its SEN services and that Enfield, although technically an outer London borough, has substantial "inner city" areas with their associated problems.
John Salisbury, head of Aylward School and headteacher representative on the council's education committee, said the issue was not one of inadequate funding for Lambeth schools, but of unfairness between the two sectors. Pounds 100,000 was the equivalent of almost four members of staff, he pointed out.
GM heads share their local authority colleagues' outrage. Geoffrey Mills, head of the 1,250-pupil Latymer School, a grant-maintained grammar, said: "We all deplore two-tier funding."
If the borough does not find the money to match the funding level of GM schools, the gap between the two sectors could get wider.