Mr Cook built up his parliamentary reputation in opposition by attacking the Tories for their use of Public Interest Immunity (PII) certificates in the affair.

Ministers invoke PII to prevent the release of particular secret documents whose disclosure is said to threaten the national interest or endanger the work of the secret services.

In opposition Robin Cook decried the use of PII as a scandal

Mr Cook has claimed PII to stop Paul Grecian gaining access to secret intelligence reports in a case that the businessman is bringing against Customs and Excise for malicious prosecution.

It will now be up to the judge in the case to rule whether the documents should be disclosed.

But Shadow Foreign Secretary John Maples denounced Mr Cook's action as "a hypocritical U-turn".

He said: "How rich in irony that Robin Cook, who in opposition championed the cause of this individual, should now, in government, with a wave of his pen, prevent Mr Grecian's access to justice."

The Foreign Office says it was its policy not to comment on PII cases.

Cleared men seeking damages

Mr Grecian was one of four businessmen connected with the Reading-based arms firm Ordtec, who were wrongly convicted in 1992 of illegally exporting an artillery fuse assembly line to Iraq via Jordan.

Some of the military fuses were allegedly to be used in Iraq's nuclear programme.

The four men were advised by their lawyers to plead guilty after the then Home Secretary Kenneth Baker and Trade Secretary Peter Lilley signed PII certificates seeking to withhold official papers relating to the case.

Saddam Hussein: UK firms supplied his regime with weapons

The case had strong echoes of the Matrix Churchill affair - which led to Sir Richard Scott's arms-to-Iraq inquiry.

Mr Grecian had been passing information to the security services about Saddam Hussein's weapons procurement programme, including details of the Iraqi supergun.

His conviction and those of his co-defendants were eventually overturned by the Court of Appeal in 1995.

Mr Grecian and his father John - who was also charged, although the case against him was later dropped - are now suing Customs and Excise, which brought the prosecution, for damages.

They argue that the prosecution was malicious as Customs was aware that the Tory government was turning a "blind eye" to arms sales to Iraq and that Mr Grecian had been assisting the security services.

The PII claim issued by Mr Cook covers four intelligence reports relating to the role of the security and intelligence agencies in events before the initial prosecutions.

In his certificate, Mr Cook said he had personally examined the documents and was satisfied that disclosure would cause "real harm" to the work of the agencies.

However, the Grecians' solicitor Lawrence Kormornick said it was important that there was full disclosure of all material relating to the case.

"We are concerned to get full and adequate disclosure of all documents to see who knew what and when about exports to Iraq and the information provided by Paul Grecian to the security services," he said.

"This is extremely relevant to the pleaded issues in the Grecian cases of malice and reasonable and probable cause."

Echoes of Matrix Churchill

Matrix Churchill directors passed vital information to the UK government

In the Matrix Churchill affair directors of the Coventry-based engineering firm were prosecuted for selling Iraq machine tools which could be used to make weapons.

Several Tory ministers signed PII certificates to try to stop the disclosure of documents which showed that the defendants had been working for British secret services.

However, the judge in the case refused to accept the certificates and the prosecution collapsed in 1992.