THE Government's announcement that the UK's terror threat has been raised from substantial to severe was accompanied by news of plans to tighten laws to help prevent people travelling abroad if it is thought they may be involved in criminal activity.
The apparent arbitrariness of threat levels and the guarded nature of the security services do not lend themselves to openness which, given the circumstances, is understandable.
Home Secretary Theresa May explained that while an attack on the UK was "highly likely" there was no intelligence to suggest one was "imminent". The opaqueness of such pronouncements is problematic, especially when terror threats are being used to justify measures that would potentially restrict civil liberties.
However, the Government is acting on judgments of potential risks made by the Joint Terrorism Analysis Centre, independently of ministers.
There plainly is a serious concern about radicalised British citizens travelling to Syria and Iraq, apparently to fight with the forces of Islamic State, and what might happen when they return home.
The horrific beheading of journalist James Foley, allegedly by a London-based former rapper, was a clear indication that such concerns are real and substantial. Such citizens, potentially now trained and indoctrinated by individuals with an anti-West agenda, could easily bring a threat to home soil and their return could be hard to prevent.
The Government says UK citizens can expect to see little difference under the heightened threat level and the public are not being advised to make major changes to their behaviour. In that context it is hard to see what purpose the announcement serves other than to make people anxious. An increase in police presence and armed patrols may add to that anxiety.
Meanwhile, it is difficult to see what action the Government itself can take to prevent would-be radicals - 500 of whom have already travelled to fight in Syria, according to David Cameron - from going.
Stopping and screening people who are flying there is an obvious step, but what about those travelling to neighbouring countries, such as Turkey?
Mr Cameron warns Britain and other Western societies are threatened by "a poisonous ideology of Islamist extremism that is condemned by all faiths and by all faith leaders",
It is extremely important the last part of that comment is understood, especially in combination with the advice to the public to be vigilant.
Most of us have little way of spotting a genuine threat. Yet through ignorance, there is a danger that the threat from Islamic extremism is equated in the minds of some with a threat from Muslims in general.
Unjustified restrictions on the civil liberties of one religious minority, or indiscriminate suspicion of that minority, are not only unfair. They risk fanning resentments among those who should be our allies.