Jack Straw, in ruling against the release of cabinet minutes relating to the UK's going to war in Iraq, has violated a key principle of the British constitution. That principle is nemo judex in sua causa: no-one should be a judge in his own case. Mr Straw stands personally to gain by the continuing secrecy of the cabinet papers.

The war in Iraq has been described by Lord Bingham of Cornhill, the former senior law lord, as "a serious violation of international law". The British public has a legitimate interest in knowing how its government came to have entered it. Jack Straw was Foreign Secretary at the key time.

If there was something unlawful taking place how can one of the possible culprits be the person who makes a quasi-judicial decision that the evidence must remain secret? That is the equivalent of a police suspect telling the police there will be no investigation as there is nothing to worry about.

The point is not narrow and academic. The war in Iraq has resulted in tens of thousands of deaths, massive social upheaval and has been condemned as unlawful by many eminent international lawyers and senior judges.

The principle of cabinet confidentiality is an important and precious one. It is quite right that cabinet members should be able to engage in full, frank, and robust discussion safe in the knowledge that their individual views will not be disclosed. Once they have decided a point all must promote that decision (even those who dissented from the view that was eventually adopted) and take a single collective stance. That is the principle of collective responsibility. If ministers' dissents in cabinet were the subject of regular disclosure it would destroy the valuable working practice of government via collective ministerial debate.

But if the legislated principles of freedom of information are to mean anything, they must be applied in a case such as the current request. Six years after the decision to go to war in 2003, there is no current issue of national security to prevent disclosure. That is why both the Information Commissioners and the Information Tribunal have ruled that the papers should be released.

The principle that no-one should be a judge in his own case is embedded in British governance. It applies to judges and stops them ruling in cases in whose outcome they might have a social or financial or interest. They can't rule in a case, for example, in which one of the parties or witnesses is a relative of theirs or a company in which they have shares. The same principle applies to people acting in a judicial role or — like Jack Straw — people making a major legal decision with significant consequences.

Professor Gary Slapper is Director of the Centre for Law at the Open University

Explore Law

• Columnists

• Law Panel

• Law Reports

• Student Law

Times Recommends

• BGC 'set aside £40m to lure Tullett brokers'
• Legal aid review to ensure value
• Fears as 21 magistrates' courts face closure