Proposals in the children's green paper to use children's NHS numbers as unique identifiers to enable the exchange of information between agencies and authorities could be hindered by legal concerns, it was revealed this week.

Bolton Primary Care Trust, which is involved with one of the government's 10 identification, referral and tracking pilot projects, is considering whether it could be acting unlawfully if it shares information with Bolton Council as a part of the project.

The council has asked the PCT to put the name, address, date of birth and gender of all the children it has contact with on an IT database that would be accessible to agencies involved, such as social services.

But the PCT is concerned whether it has the statutory power to provide such information. It is considering legal advice that there is a "respectable argument" for the details to be passed over. But Bolton's IRT project manager John Morrissy said "this is an opinion" and called on the government to provide a legal framework to improve the situation.

Andrew Cozens, president of the Association of Directors of Social Services, said the issues raised in Bolton could hinder the green paper's proposal. "It could be a fundamental problem given that the unique identifier is probably going to be the NHS number," he said.

Kensington and Chelsea's IRT pilot project has put plans for a similar database on hold following Bolton's legal advice (news, page 9, 23 October).