Eleven of London's 33 boroughs have more than 31 pupils in each class, compared with just 27.5 per cent of infants nationally.
But Kingston, where more than 70 per cent of children are taught in large classes, was the second-best performing authority, according to primary league tables published last month.
Redbridge and Bromley, where more than half of pupils are taught in overcrowded classrooms, also scored highly in the London table of national tests for 11-year-olds.
The findings, which do not take into account social and economic factors affecting many schools, will be seized upon by the Secretary of State for Education, Gillian Shephard. She has continually stressed that teaching methods are more important than the number of children per teacher.Reuse content