Admiral Lord West of Spithead was correct yesterday, on both occasions. First, the right attitude to any proposal for extending pre-charge detention for terrorism suspects beyond 28 days is: “Prove it”. Or, as Lord West said: “I want to be totally convinced, because I am not going to go and push for something that affects the liberty of the individual unless there is a real necessity for it.”

Secondly, there is, as he later added, a case for an extension for certain complicated plots. Despite all the gaffe stories yesterday, the two positions are compatible. The absolutists on both sides are wrong. Tony Blair was defeated in the Commons two years ago over 90-day detention (a very rare defeat for any government with a comfortable working majority) largely because of his cavalier dismissal of civil liberty worries. For him, being tough on terrorism always came first.

On the other side, some civil libertarians are wrong to rule out any extension of the 28-day limit.

It is not good enough just to incant terrorist threat, as Mr Blair used to do. The level of proof should be high. The case will, anyway, have to be very convincing to win support not only in the Commons, but particularly in the Lords, where the idea faced very strong opposition during a debate on Monday. Gordon Brown recognises these constraints and is approaching the issue in the right way. He argues that the complexity of some plots – with multiple false identities and passports, numerous addresses and thousands of computer disks – may require a longer period for investigation by the police before charges can be made. But the advocates have to produce evidence about why the current limit is not enough and why the problem cannot be addressed by parallel proposals for postcharge questioning and use of intercept evidence (still under review).

Any extension would have to be made exceptional. However, the existing powers in the Civil Contingencies Act for longer questioning look inappropriate, since they would involve declaring a state of emergency, which would raise the stakes. There is also the risk that an extension would be depicted as internment: hence Mr Brown’s emphasis yesterday on safeguards, including not just going to a judge, but also the Director of Public Prosecutions being involved, as well as reports to the Commons and a study by the independent reviewer. Mr Brown said he hoped that the Home Secretary would win a cross-party consensus. That may be wishful thinking. Several parliamentary inquiries have been held in this area, but there is a case for a further one focusing only on the 28-day issue.

This is just one aspect of a wideranging national security strategy. It was a classic Brown exercise, the super-swot who has read every book and report and talked to everyone. He is correct that toughness is not enough and isolating extremists is equally important. But there were at least 50 initiatives, reviews and advisory groups in his 20-minute statement yesterday. Most can be justified in their own terms. But the question, as always with Mr Brown, is whether he is trying to do too much: whether quantity may be the enemy of effectiveness.

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