More Oxfordshire primary pupils are crammed into "nightmare" classes of 36 or above than in any other South East authority, according to Government figures.

Although the county's average class size of 25.7 remains below the national figure of 26.3, a total of 626 pupils have been taught in classes of more than 36 pupils with one teacher this year.

Ironically, teaching unions have blamed a Government initiative designed to reduce teacher workloads for the creeping class sizes.

The provisional figures, published yesterday, are based on roll numbers in January, and show Oxfordshire as the worst in the region. West Sussex had the second highest with 599 pupils, followed by Hampshire with 444. Some authorities, such as Portsmouth, had no children in classes this large.

A further 5,739 Oxfordshire pupils are being taught in classes of between 31 and 35 this year.

Schools cannot start the year with classes of more than 30 infants (children under seven) but can, in certain circumstances, add to numbers later in the year.

The Government's workforce remodelling agreement, introduced in September last year, requires schools to release 10 per cent of teachers' time for planning, preparation and assessment (PPA).

Bob Martyn, spokesman for the Oxfordshire Association of Teachers and Lecturers, said the number of complaints from teachers about class sizes was increasing.

This had put pressure on school budgets, forcing heads to make savings elsewhere by cutting support staff.

Mr Martyn said: "Class sizes have been creeping back up.

"On top of that, teachers have an increased number of children with special needs and their teaching assistant has been taken away to help provide PPA time so they have more behaviour issues to deal with.

"It's a nightmare for any teacher to have that sort of class.

"Trying to control all these different groups at once and seeing every child has got work at the right level that's the sort of thing that makes teachers burn out with stress.

"Rather than the work load improving, teachers are feeling under more pressure and are not meeting the needs of the children in their classes."

Michael Waine, Oxfordshire County Council's cabinet member for schools improvement, said it only compared itself to 10 statistical neighbours, not regional neighbours. These figures put the county in a slightly better light, but it is still among the worst.

Mr Waine said: "It is good that Oxfordshire is doing better than the national average in terms of class sizes at Key Stage Two.

"A class with more than 36 pupils will often be taught in smaller groups for a proportion of the day.

"I am concerned that there are a growing number of schools with larger classes and I'm also concerned about the impact of PPA. We will be working with the education unions on this issue.

"As an authority, we can only advise schools."