The House of Lords has rejected former MI5 agent David Shayler's bid to use a "public interest" defence in his upcoming "state secrets" trial.

The law lords unanimously said there was no incompatibility between the 1989 Official Secrets Act, under which Shayler faces prosecution, and Article 10 of the European Convention on Human Rights guaranteeing "freedom of expression".

Mr Shayler is accused of disclosing state secrets in 1997 in a series of newspaper articles about alleged illegal activities and incompetence in the security services.

Lord Bingham of Cornhill said: "The crux of this case is whether the safeguards built into the Official Secrets Act are sufficient to ensure that unlawfulness and irregularity can be reported to those with the power and duty to take effective action, and the power to withhold authorisation to publish is not abused and that proper disclosures are not stifled."

In his opinion the existing procedures properly applied, including the right to seek judicial review, "provide sufficient and effective safeguards".

Lord Hope of Craighead, Lord Hutton, Lord Hobhouse of Woodborough and Lord Scott of Foscote agreed, dismissing Mr Shayler's challenge.

The former agent's criminal trial is due to take place at the Old Bailey later this year.