There is something odd about the fact the Metropolitan Police Commissioner launched Counter-terrorism Awareness Week by claiming "four or five" terror plots have already been stopped this year.

Sir Bernard Hogan-Howe's point was to compare this against an annual average of one plot in previous years. Yet it also serves to highlight the vagueness of the details we are given about the threat from terrorism. Was it four or five?

This matters because, increasingly, such threats are being used to justify increased powers for the police and security services. Home Secretary Theresa May insists her latest proposals are carefully thought out and in the interests of keeping us all safe at a time of considerable danger. New laws will require internet service providers to retain information which will enable individual computer users to be identified, while schools, universities and councils will face new duties to counter radicalisation.

The international situation, particularly the conflicts in Iraq and Syria and the brutal rise of Islamic State, has led Britain's terror threat level to be raised from substantial to severe and Mrs May says the risk is "perhaps greater than it has ever been". But there are few specifics. It is understandable that intelligence should remain secret and only a limited amount can be revealed about counter-terrorism tactics. And any government would be failing in its duty if it did not do all it could to keep us all safe. However, there are legitimate concerns about ever increasing restrictions on individual liberties and the right to privacy, applied for reasons that cannot be properly scrutinised.

The problem is that the other political parties, fearful of being seen as weak on security, might not fully hold the Government to account. That is why it falls to organisations such as Liberty to point out that evidence and intelligence should lead our response to terrorism, not blanket surveillance, or there is a risk we fan the flames of extremism by adding to resentment among groups in society that feel they are being targeted unjustly.

It will never be possible to eliminate all threats completely. The eyes and ears of the public are among the best defensive tools available. The police acknowledge that, without public support and vigilance, they cannot defeat terror. That is why the Government's Counter-terrorism Awareness Week is valuable. But the public should be given more information on the nature of the threat, so we can balance this against the cost of any new laws to counter it.