Many state-funded schools are breaking the government's new code on fair admissions, with some asking parents to make a financial contribution before accepting an application, Schools Secretary Ed Balls said on Tuesday.

The code, which came into force in time for secondary school places granted last week, bans schools from selecting children on the basis of academic ability or social class.

Schools can no longer interview children or parents before admission and have to give priority to those in care.

But a survey of three local authorities in Northamptonshire, Manchester and Barnet in north London found a "significant minority" of schools were not complying.

Balls said he would tighten up regulations, requiring local authorities to report each year on the legality and fairness of admissions policy at each school in their area.

The code is currently largely policed by parents making objections where they feel admissions are unfair.

But Balls said that across England there had only been 79 objections from parents to the Schools Adjudicator, who has the power to order changes in the ways pupils are admitted.

Balls said he would publish a guide for parents on admissions and appeals, and extend the period during which objections could be made to the adjudicator.

As well as asking parents for financial contributions, banned practices discovered in the three areas surveyed included:

- asking about the marital status of parents, their jobs and income

- giving priority to family members who were not siblings currently at the school

- interviewing pupils

- not giving priority to children in care.

Balls said he was surprised by the findings, but stressed that the large majority of schools in the areas surveyed had complied with the code.

Data published on Tuesday showed that 82 percent of parents received an offer of a place for their children at their first choice secondary school for the 2008/9 academic year.

The code was introduced to assuage concerns among Labour backbenchers who feared that provisions giving schools greater autonomy would lead to covert selection and work to the disadvantage of poorer children.