Leading article: Tough talk and empty gestures

Latest indications from Westminster suggest Gordon Brown will succeed in his attempts to extend the time that terror suspects can be detained without charge. Apparently, enough Labour MPs have been won over by a series of concessions that are more limited than they seem. Perhaps they are also influenced by the likely dire political consequences of a Commons defeat for the Prime Minister over the issue.

These are inadequate reasons for a change of heart over such an important issue of principle. The concessions are not significant. Indeed, it is difficult to see what precisely has changed since the proposals were first brought forward. Mr Brown has always made clear there would be a series of safeguards in the event of an extension being triggered. Evidently, the Home Secretary, Jacqui Smith, delivered an impressive performance when she addressed Labour MPs at a private meeting on Monday evening. But again the quality of a political performance should not determine the outcome of next week's vote.

The substance of the arguments remains unchanged. The Government wants a substantial extension when there is no clear evidence such a move is necessary. The former Attorney General, Lord Goldsmith, is unconvinced. Tony Blair's old ally, Lord Falconer, sees no case. The Commons Home Affairs Committee saw no decisive arguments in favour, having heard from an array of witnesses. Even the former Home Secretary, Charles Clarke, has said it would be wiser for Mr Brown to drop the measure. The Government has been unable to give an example of a single situation in the recent past where an extension would have helped bring suspects to trial.

The relationship between civil liberties and national security is complex and has been made more so by the threat posed by terrorism. For a prime minister, the responsibility of seeking to protect a country from such a threat is awesome. But Mr Brown had no obvious immediate need for reviving this highly charged issue. Not so long ago his predecessor, Tony Blair, was defeated in the Commons on an admittedly far more sweeping proposal, the first time he had lost a vote as prime minister. The arguments that prevailed then apply now.

They are not addressed by a reduction from Mr Blair's 90 days to Mr Brown's 42. Both are arbitrary figures. There is already legislation that permits an extension in an emergency. Ministers insist their proposals would apply only in unusual circumstances. So why do they not make use of existing arrangements which are supported by all the political parties? Part of the answer is that there is a degree of posturing, an attempt to look tough. Labour MPs who had doubts before should have doubts still.