The Funding Agency for Schools is next week expected to reveal serious problems in the capital which could cost the Government some Pounds 200 million to remedy.
They are disclosed in a report into the 20 - out of the 33 - London boroughs where it shares or has exclusive responsibility for secondary places. A bleak picture is painted in the draft copy of the report obtained by The TES. It highlights particular difficulties in Bexley, Enfield, Sutton and Waltham Forest where the authorities will be short of between 1,000 and 2,700 basic-need places by 2003.
At best, the report suggests, there will be a deficit of 9,400 places for 11 to 16-year-olds across the 20 boroughs by 2003 - at worst it could be more than 30,000. This is the equivalent of between 10 and 37 schools.
Although it is understood the FAS does not recommend how many schools should be built, last summer it suggested that London could get 19 new grammars.
Its findings, due to be published next Friday, are based on figures supplied by local authorities, the Office for National Statistics and the London Research Centre.
They do not include the extra places ministers say must be made available in schools to provide choice and diversity. Five per cent flexibility would require another 10,000 places, at a further cost of Pounds 65m.
The 9,400-place shortfall - which would cost Pounds 61m to remedy - is based on the Department for Education and Employment's own method for calculating basic need.
Using its "more open enrolment" system which provides a measure of the physical capacity of the whole school, a shortfall of 22,500 places for 11 to 18-year-olds is predicted, at a cost of Pounds 146m.
But the FAS said : "Such a deficit would, in practice, be partly offset for as long as some schools continued to enrol above their measured capacity."
Figures obtained from LEAs by the Agency on pupil numbers and school capacity, and on which both estimate the future need for places, point to a 15.3 per cent increase or more than 30,000 pupils.
Every 1 per cent growth in the number of pupils aged 11 to 16 equates to around 2,000 pupils with the DFEE allowing a rough average of Pounds 6, 500 for each new school place which needed to be created in London. This would mean around Pounds 200m would have to be found to meet demand if the local authorities, who have a low error rate, are right on their predictions.
The report covers just two-thirds of the London boroughs and Chris Waterman, education officer with the Association of London Government, said: "What is needed is a proper London-wide study, a sensible look at what our needs are, where schools ought to be built and money provided for them. How on earth can a remote quango based in York plan schools in the capital?" London authorities bid for Pounds 370m for capital for schools this year, but were awarded just Pounds 56m by the Government.