An MP today won a legal test case challenging the Government's blanket ban on MI5 releasing material it holds on individuals.

The "landmark victory" for Norman Baker - the Lewes MP and a home affairs spokesman for the Liberal Democrats - came with the first-ever ruling from the Data Protection Tribunal's new National Security Appeals panel.

After the decision, announced by panel president Sir Anthony Evans at the High Court in London, Mr Baker said: "I am delighted with the judgment. It is a landmark decision and a victory for the individual against the state."

Mr Baker added that the ruling was a recognition that it was "improper and inappropriate" to grant a blanket exemption to the security service in its efforts to maintain national security.

He emphasised that he fully backed the security services' need to maintain secrecy on the basis of national security but that every case needed to be assessed on its own merits.

He expressed the hope that if any files did exist they would now be made available to him.

In July 2000, Mr Baker applied under the Data Protection Act to see any material that the security services held on him.

He was told any files which may exist - and the spymasters refuse to confirm or deny they hold any details on Mr Baker - were exempt from the Data Protection Act and did not have to be revealed.

Mr Baker asked the National Security Appeals panel to overturn the decision on this blanket ban.

MI5 holds about 440,000 files, 290,000 of which are on individuals.