Rarely are the rights of an individual pitted so acutely against the interests of the public as when the authorities decide to expose secrets in someone’s past.

When, for example, a couple convicted of violent sexual assaults on children decided to live on a campsite, their right to keep details of previous offending secret was jeopardised by the police, who decided to inform the campsite owner.

In those circumstances, the Court of Appeal said a decade ago in “AB”, a careful balance had to be struck – disclosure of such inflammatory information had to be confined strictly to the purpose and extent necessary to protect the pubic. 

The balance is even harder to strike when the information does not arise from any criminal convictions. No job applicant really wants their private life disclosed to an employer, and when the only basis for such disclosure is that the police are of the opinion it “might be relevant”, the lines become blurred.

This was the experience of L, who today received judgment from the Supreme Court in her case against the Police Commissioner. 

 L was dismissed from her job as a school assistant in 2004, after an Enhanced Criminal Record Certificate revealed that her son had been placed on the child protection register, and that L had been regarded as “uncooperative” with social services.

The result of disclosing these details, L said, was that she would be prevented in the long-term from any form of work involving care for or contact with children.

So the Court considered how the police are to resolve this tension between the privacy rights of an employee, such as L, and the public interest – described by Lord Hope in language of qualified rights as, “a pressing social need that children and vulnerable adults should be protected against the risk of harm.”

“It is of the greatest importance that the balance between these two considerations is struck in the right place”, Lord Hope added. 

The Court has not always got it right when it comes to striking this particular balance between the right to privacy, and the interests of society which may justify interfering with it.

In S and Marper – the case which has lead to the ongoing redesign of the National DNA Database – the Court got the balance wrong. The House of Lords, the European Court of Human Rights concluded last December, was over-impressed with the claims of the police about how the Database helped them to solve crime, as against the serious privacy implications of indefinitely retaining DNA samples and profiles.

No doubt L – who failed to have the information in question removed from her ECRC – is today feeling that the Court are still getting that balance wrong. She has, throughout three years of litigation, argued that her long-term inability to work in schools as a result of the ECRC is a disproportionate outcome.

But despite dismissing L’s appeal, the Court was clear that the police need to do more to balance the privacy rights of individuals who may find damaging information disclosed on their ECRC.

“The rationale for disclosure should make it very clear why the human rights infringement outweighs the risk posed to the vulnerable group”, said Lord Hope.

And, where there is doubt, Lord Hope added, a presumption of disclosure was not good enough – the individual concerned should be able to make representations.

“The risks in such cases of causing disproportionate harm to the applicant outweigh the inconvenience to the chief constable”, Lord Hope said, anticipating a lack of enthusiasm among the police at the prospect of inviting individuals to put their case across.

In other words, where there are competing interests of protecting vulnerable children, protecting private information, and expecting the police to work harder in weighing the two – there is only one clear loser. Sorry, officer.

Afua Hirsch was a barrister, and is now the Guardian’s legal affairs correspondent. Her latest feature in The Guardian, on the BNP’s Question Time appearance, Jan Moir and freedom of expression, is here. You can also follow her on Twitter.