A Government-backed change to school admissions could reduce opportunities for pupils to go to secondary schools outside their local education authority.
The London borough of Camden this week launched discussions on giving priority for places at its secondary schools to children already in its primaries.
The changes would curb the large number of middle-class children who cross the border from neighbouring boroughs such as Islington and Haringey to escape schools where exam results tend to be lower.
Camden's aim is to improve transition from primary to secondary, and - consequently - to improve standards at key stage three and four. Currently, only around 64 per cent of the borough's children stay on in its secondary schools.
The Department for Education and Skills has told the council it believes the change to admissions would not contravene the 1989 Greenwich judgment, a landmark High Court decision which held that schools should take eligible pupils who live nearest - regardless of local authority boundaries. It gave the go-ahead to cross-border flows of pupils in London and elsewhere. Both DFES and the council believe the proposed admissions criteria is unique, although a few other education authorities, such as Newham, do use feeder school links as a criteria.
Camden has enough places in its 10 secondary schools to accommodate all the children leaving its primary schools.
Parents groups claim they are already leading campaigns in six London boroughs, where there are concerns about shortages of secondary places.
In North Lewisham, parents say there are only 1,030 secondary places for the 1,500 children leaving primary, although the London Education Authority says that, overall, it has enough places for all its pupils.
Louise Irvine, leader of north Lewisham's New School for New Cross campaign, said plans to set up a sixth form centre - bringing together the sixth forms of four secondaries, would make things worse.
But a council spokesman said the centre, which will not open until September 2002 at the earliest, would free up another 100 places for year 7 pupils.