The issue was raised during a House of Commons debate initiated by Liberal Democrat MP Steve Webb, who cited the case of a girl in his Northavon constituency who was denied a place at her local primary school because she would have been the 31st member of a class.

Under the School Standards Act, enacted to fulfil a Labour manifesto pledge, infant class sizes are limited by law to 30 pupils.

Mr Webb asked the minister: "Do the rules have to be this rigid and this strict? Is there a way of making the rules more relaxed?"

Ms Morris conceded that the legislation would cause some parents to be denied their first choice of school.

"I acknowledge that the whole issue of admissions is an incredibly difficult one...for a parent, all that matters to them is their child," she said.

But the minister added that the government remained committed to its pledge to bring class sizes for that age group down to 30 or below, and was on course to hit the target 18 months ahead of schedule.

"That's the difficulty of dealing with this area, because parental choice is also about the rights of other parents to have a reasonable class size."