Immigration is putting schools under immense pressure as they are having to teach record numbers of children whose first language is not English. One in seven pupils at primary school and more than one in ten at secondary school have an overseas language as their mother tongue.

New statistics also show that an increasing number of schools are breaking the law by cramming more than 30 pupils into infant classes. Two hundred did so this year, compared with 130 last year.

Nick Clegg, the Liberal Democrat leader, said: “The problems stem from the Government’s failure to plan for population changes – not from the existence of migrants.”

The data show a decreasing white school population, from 82.1 per cent in primary schools in 2004 to 80 per cent this year. This was mirrored by the fall in the number of pupils who are native English speakers, from 89 per cent of primary school children to 85.5 per cent over the same period.

The National Union of Teachers said that schools needed more money to meet the needs of children whose first language was not English.

Teachers’ leaders defended schools that had broken the law on class sizes. Mick Brookes, general secretary of the National Association of Head Teachers, said that the Government needed to be less rigid about class sizes for young pupils. “One more child than 30 means you need another teacher,” he said. “This creates a financial and logistical problem for schools.”

Jim Knight, the Schools Minister, said: “Under the Tories, 480,000 infants were taught in classes of 31 or more pupils. Today that’s down to 6,500 and only around one in 250 infant classes are unlawfully over our legal limit. We are making sure that local authorities and schools take immediate action in each of these cases.”

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