According to analysis of Department for Education (DfE) figures on schools, pupils and their characteristics by the Labour party, some 40,000 primary children are in classes with more than 36 pupils and over 16,000 are in class sizes of at least 40.
The South East of England is reportedly 'worst hit', with more than 90,000 primary school pupils in classes over 30.
The findings, which Labour says indicate that the Conservatives have broken their promise on 'small schools with small class sizes', also show the number of 'titan' primary schools (schools with over 800 pupils) has increased almost seven-fold since 2010.
Highlighted by the Labour leader Jeremy Corbyn in a speech in the Conservative constituency of Cardiff North today, the analysis reveals that the pressure on school places is now starting to affect secondary schools, with an increase in the number of pupils in 'very large classes' in the last year.
The Labour party warns that the situation threatens to get worse with the cuts to school budgets, forcing schools to expand classes further. It says that various teaching unions have reported that many schools have been forced to do this already.
Mr Corbyn said, 'Seven years of Tory failure and broken promises have left our schools in a terrible state. Hundreds of thousands of our children are paying the price, crammed into classrooms like sardines.
'The Prime Minister herself has said that super-sized classes are proof of a school system in a crisis. And that’s what we’ve got on the Tories’ watch.
'Labour will stand up for all children by building a schools system for everyone, keeping class sizes down and making sure schools and teachers have the resources they need to ensure that every child, whatever their background, has access to a world-class education.'
Shadow education secretary Angela Rayner said, 'This situation is becoming unsustainable - too many children are being taught in classes which are simply too big.
'The system for school place planning is broken. The Tories need to let go of their unjustified fixation with Free Schools, but instead they have relaxed the rules so even more can be built in areas where there is no demand for places. Free Schools are clearly not addressing the growing pressures on schools.'
The release of the findings by Labour follow a pledge by the party last week that the next Labour government would fund free school meals for all primary pupils by charging VAT on private school fees.