The NUT wants primary school classes limited to 26 pupils

The Department for Education and Skills said the figure had increased from 740 to 910 in England since last year.

But the average of 25.6 children per class had remained the same. Schools Minister Jacqui Smith said there had been "significant progress".

The Lib Dems called the figures "deeply worrying". The Conservatives said they were "moving in the wrong direction".

Legal limit

The government has changed the law to limit class sizes to 30 pupils for five to seven-year-olds.

Only those given special permission are allowed to exceed this.

DfES figures show the number of classes of five to seven-year-olds with more than 30 pupils has risen from 740 to 910, or 1.2% to 1.6% of the national total.

But the number of cases where the school did not have permission fell from 530 to 390.

Once again the government is failing to deliver the basics for young children Sarah Teather, Lib Dems

Ms Smith said: "This year the number of classes that contravene class size regulations has fallen.

"However, there has been a small rise in the number of classes - with valid exceptions - where numbers exceed 30 children.

"The government has a range of legal powers that can be used to ensure that schools fulfil their legal obligations on class sizes, and there should be no doubt that we will not hesitate to use them where necessary."

The National Union of Teachers has called for the pupil limit to be reduced to 26 per class.

Labour's promise

A spokeswoman said extra investment in staffing was needed to ensure a better teacher-to-child ratio across England.

The DfES figures show that, for primary schools as a whole, the average class size has risen from 26.2 to 26.3 pupils.

For secondary schools the average has fallen from 21.7 to 21.5 pupils.

The DfES also revealed that the number of full-time teaching posts - or the equivalent made up of part-timers - has risen by 3,500 to 435,400 since last year.

Ms Smith said: "More teachers and more support staff is evidence of the positive impact that our record investment is making on standards in our schools."

Shadow Education Secretary David Willetts said: "Labour made a promise to parents that they would abolish infant class sizes of more than 30.

Classroom attention

"Tony Blair even claimed last year to have delivered on it. Today's figures show that there are 30,000 infants in classes of more than 30, and the trend is moving in the wrong direction."

Lib Dem education spokeswoman Sarah Teather said: "These figures are deeply worrying. Parents want to know that the teacher is going to be able to pay attention to the individual needs of their child.

"The bigger the class the harder it is to give individual children attention. Smaller class sizes create a better learning environment and help foster better behaviour within the classroom.

"Once again the government is failing to deliver the basics for young children."