The controversial law guaranteeing a 'named person' for every child in Scotland could breach young people's human rights, a legal charity has warned.

Clan Childlaw is to tell the UK Supreme Court next week that agencies such as health, education and social work will be justified in sharing information about a child merely on the basis of concerns about their wellbeing, rather than the previous much tougher test of being 'at risk of significant harm'.

This means children can have virtually no expectation of privacy or confidentiality, the charity says, breaching article eight of the European Convention on Human Rights.

Clan Childlaw gives legal help to children and young people in Scotland, and is intervening in the judicial review of the Young People (Scotland) Act 2014, which has been brought by the Christian Institute and other groups.

These groups are primarily concerned that the appointment of named persons - usually headteachers of school age children and health visitors where a child is pre-school - is an unwarranted intrusion on family life. The court has agreed to hear an intervention in the case by Clan Childlaw, meaning judges recognise it could provide helpful new information. The case is to be heard on Tuesday and Wednesday next week.

Alison Reid, Principal Solicitor at Clan, said the act was vague about the conditions where a child's confidential information could be disclosed, but generally made it too easy to share information, resulting in the danger of an unlawful interference with a child's right to privacy.

She fears that because information can be shared even if the child does not consent, children could shun vital services that might help them in a crisis, or simply needing advice, rather than risk confidentiality being breached.

She said: "The Act drops the threshold from the widely understood child protection test of “risk of significant harm” to a much lower one around concern for a child’s “wellbeing”, which involves a highly subjective judgment on the part of the Named Person and others as to whether to share information.

"There is a serious risk that the overriding of confidentiality when there is no child protection concern will lead to children being reluctant to engage with confidential services."

This could lead to some failing to access the help they need, she said.

Ms Reid added: “We all want to make sure that children and young people in Scotland are protected and recognise that when child protection issues arise, these need to be shared appropriately amongst professionals. However, where there are no child protection concerns, a child, like anyone else, should be entitled to a level of confidentiality when accessing advice."

Clan Childlaw's advocate will try to persuade the judges - including Baroness Hale, of Richmond, who is known for an interest in children and human rights - that sections of the act relating to sharing and disclosing of information could be changed, to render it compatible with article eight of the EHCR.

However the groups which originally brought the case are looking for the law to be thrown out altogether.

Colin Hart, director of the Christian Institute, said: "We would endorse Clan Childlaw's concerns. Thhe named person scheme is all about the free flow of private information about children and about families in a way that to us is clearly illegal."

He said noone would question the need for information to be shared if there was a disclosure of abuse of a child or another urgent threat to their safety, but that otherwise the principle of consent should be preserved.

He denied that the Christian Institute and Clan made odd bedfellows, adding : "We are working with people we wouldn't necessarily agree with on other things because they agree this scheme is over the top."

"Lowering the bar for information sharing to being about a child's 'wellbeing' which merely means 'happy'. If a named person's own view is that it might lead to being happier, then the child won't be able to object."

A Scottish Government spokesperson said: “The Court of Session has twice rejected the petition against Named Person on all grounds and ruled it did not contravene ECHR rights or EU law.

“We have been clear that information should only be shared in a manner that is proportionate and respects the views of children and young people and existing legal frameworks. The Scottish Information Commissioner’s Office has supported the information-sharing provisions within the Act and accepted that they are fully compatible with existing law.

“The Scottish Government continues to defend the appeal.”