It may not be the Justice Secretary's intention to undermine one of the fundamental tenets of an open legal system. But his proposal to expand the use of secret evidence in Britain's courts nonetheless threatens to do so.

Granted, the wider application of so-called Closed Material Proceedings – under which sensitive material can be shown to a judge without being revealed in public – would only apply to a small number of civil cases. And granted, the changes would allow for better use of evidence from the intelligence services (particularly in terrorist cases) while maintaining national security.

There are, of course, also high-profile cases which themselves argue for reform. The most compelling is that of Binyam Mohamed, the former Guantanamo detainee paid £1m compensation over claims he was tortured with the complicity of the British Government. According to the security services, it was impossible to fight the allegations without the use of intelligence too dangerous to reveal.

The Mohamed case may be concluded, but there are 27 more in the pipeline that raise similar issues, says Ken Clarke. Even so, there is still no possible justification for creating a situation where suspects may not know the full extent of evidence against them, and cannot therefore defend themselves.

No less alarming is that the new rules would also apply to inquests, raising the possibility that post-mortem examination details deemed to be a matter of national security could be kept from the deceased's family. One need think only of the shooting of Jean Charles de Menezes to appreciate the risks such powers raise, however carefully circumscribed they may seem to be.

The Justice Secretary is right that national security and the protection of intelligence sources should be top priorities; and right, too, that the status quo is far from ideal, when critical evidence in highly sensitive cases may not be heard. But the reforms he proposes are a compromise too far. Even the slightest tilt towards the closed courts and secret justice so favoured by despots is not a price worth paying. Mr Clarke must think again.