The government is being urged to increase infant class size limits in order to save money.
In a letter circulating among London councils, Sutton Council chief executive Niall Bolger said increasing infant class sizes to 32 would save funds without harming education. The current limit on infant class sizes is 30.
Bolger said the £7 million being spent by Sutton Council to fund additional classes for the start of the next school year in September would not be needed if existing limits were scrapped. He stressed that the idea was not council policy but was in fact "basic" research.
"Increasing class sizes is not a Sutton Council policy or something that has been discussed at a political level," he said.
"There is a dreadful shortage of primary school places and we can't ignore the situation, especially when our schools, which are some of the best in the country, are attracting so many families."
The existing limits on infant class sizes were introduced by the last Labour government in 1998. The party had promised to make the change in their 1997 general election manifesto.
Mr Bolger argued that the restriction was brought in at a time of "surplus places and lower population levels than we currently experience in this country".
A Department for Education spokesman said: "The law remains clear that it is illegal for infant classes to exceed 30 pupils - no parent wants their child taught in a huge class.
"We're dealing with the impact of soaring birth rates on primary schools - doubling targeted investment at areas facing the greatest pressure on numbers to over £4 billion in the next four years.
"We are building free schools in areas where there are place shortages and letting good schools expand without limits to meet demand from parents."
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