Long-time girlfriend Annie Machon has stood by David Shayler

Seeking permission to challenge the conviction, his lawyers argued in the Court of Appeal that his Old Bailey trial in 2002 was unfair because of the "unprecedented" restrictions imposed on him by the trial judge at the behest of the prosecution.

Geoffrey Robertson QC said the trial was conducted in breach of Mr Shayler's right to a fair hearing under common law and under the European Convention on Human Rights.

The 37-year-old from Middlesbrough, was jailed for six months in November 2002 for revealing intelligence service information to a newspaper.

He insisted that he was not a traitor, had not endangered the lives of intelligence agents and was motivated by a desire to expose abuses of power by the intelligence services.

He was released under licence after serving seven weeks.

Mr Robertson said Mr Shayler suffered discrimination after choosing to defend himself at the trial rather than being represented by counsel.

'Cloak of secrecy'

Trial judge, Mr Justice Moses required him to disclose in advance the questions he planned to ask prosecution witnesses in cross-examination.

Mr Shayler was denied the right to question the creditworthiness of the five witnesses, four of whom remained anonymous under a "cloak of secrecy" at the behest of the Home Secretary, said Mr Robertson.

The judge had access to "secret schedules", partly prejudicial to Mr Shayler, which he was not permitted to challenge.

The Crown admitted that most of those restrictions would not have been sought if Mr Shayler had been represented by counsel.

Yet there was no suggestion that Mr Shayler planned to "blurt out" sensitive information during the trial, said Mr Robertson.

Mr Shayler was robbed of his ancient right to defend himself in court without his statements being "vetted" in advance by prosecutor and judge.

Lord Justice Kennedy, Mr Justice Cresswell and Mr Justice Bennett reserved judgment to a later date.