The situation is most severe in outer London grant-maintained schools where nearly one in three primary and one in eight secondary-aged children are in classes of more than 30.
In local authority schools nearly one in five primary and one in 14 secondary children have 30 or more classmates, according to the London Research Centre's report Education in London: Key Facts.
The Government has earmarked Pounds 620 million to cut all infant classes to below 30 by 2001. But overall, class sizes in London local authority primaries have remained at last year's level while their GM counterparts now have more larger classes.
Despite the marked rise in the number of large classes the survey reveals a small improvement in pupil-teacher ratios: LEA secondary schools had an average of 15.8 pupils per teacher compared to 15.9 last year while grant-maintained secondaries' figure was 16.1 down from 16.4 in 1997.
Ric Euteneuer, author of the report, attributed the change to an increase in non-teaching staff. He said: "There may be more staff but they are not teaching classes. The amount of paperwork schools have to deal with is overwhelming and an increasing amount of staff time is spent on admin."
Last year's report also revealed the stark contrast between pupil populations in local authority and GM schools with the latter having a less ethnically diverse intake and fewer children with special needs or eligible for free school meals. This year the gap had narrowed but was still marked.
One third of pupils in local authority secondary schools are eligible for free school meals, 48 per cent in inner London, compared to only 21 per cent of pupils at GM secondary schools.
In primary schools 29 per cent of LEA pupils get a free meal compared to 26 per cent of GM pupils.
Redbridge has the lowest exclusion rate with no primary school pupil and only one in 588 secondary pupils being permanently excluded. The highest primary exclusion rate was in Hammersmith and Fulham (0.18 per cent) while the highest secondary rate was in Croydon where almost one in 100 children was permanently excluded.
"Education in London: Key Facts" is available from the London Research Centre, tel 0171 7875618, price Pounds 10.