Leading article: The lesser of two evils

Traditionally, there have been two arguments against using evidence from telephone tapping in British courts. Civil libertarians objected to a violation of a citizen's right not to be spied upon. At the opposite end of the political spectrum, supporters of the security services argued that public scrutiny of the methods used by our intelligence officers would reveal too much of their methods to potential terrorists.

The potency of the civil liberties argument is bound to be diluted at a time when many in the West believe we are engaged in a "war on terror". The argument from the security services has long been seriously weakened by the fact that many other countries allow such evidence without any obvious harm done to their intelligence systems.

Even so, anyone concerned with national security must take seriously the concerns of representatives of the surveillance service, GCHQ, who recently told the Parliamentary Intelligence and Security Committee that they did not believe anything proposed passed the test of doing more good than harm. Rather, they argued, making telephone, fax, e-mail and postal intercepts admissible in court would lead to a net reduction in our national ability to deal with crime and terrorism.

Britain was different, they argued, because of its close co-operation with intelligence agencies in other countries and the fact it was bound by EU rules, unlike the US or Australia. Quite how was not made clear. In any case, the moves by the Prime Minister to implement the nine recommendations of the Chilcot review should go a long way to allaying these anxieties.

The argument that phone-tap evidence would create too much paperwork was always bogus, given the very few cases of a threat to national security which come to court. But concerns that clever defence lawyers could go on fishing expeditions – demanding extensive transcripts to trawl through in the hunt for other defence strategies – are addressed by the limits Chilcot places on what the prosecution is obliged to present. The right of intelligence agencies to retain control of the material and veto its use in court is key, too, in not disclosing to potential terrorists what the intelligence services are able, and not able, technically to do.

These changes will have another important impact. They deprive the authoritarians in the Cabinet of one of the key arguments they use to insist that detention without trial should be extended from the present 28 days, on the grounds that the increasing complexity of cases means it takes longer to compile convincing evidence. Allowing intercepts will make that task much easier. If it is an infringement of civil liberties that is, in anyone's book, a far lesser evil than locking people up without charge or trial.