Shortly after news reached us of last week's massacres in Brussels, I found myself at a tea-time gathering of professional colleagues. The talk was of Brussels and little else. "It's difficult to know what more we can do to prevent such attacks," was the reaction of one member of this group. Another talked vaguely about western democracies being "open societies… You can't inspect everyone going into an airport," she opined. A third went further: "How can you check people going to the theatre, or a restaurant? It's just not feasible."

Of course it is feasible. Of course you can inspect everyone going into an airport. Or a railway station. But do you, or do the governments of the western democracies, feel sufficiently motivated to put these security measures into practice?

Having asked these questions, I shocked my colleagues by revealing that there are no less then 11 security and inspection checkpoints on the approach to and inside Ben-Gurion airport. That every railway station in Israel has at least one security guard. And that Israelis know that their bags - and possibly their persons - may be inspected before they are allowed into a cinema or restaurant. Or even a synagogue.

None of these measures is one hundred per cent foolproof. But, cumulatively, they have made Israel a much safer place (at least at the present time) in which to live than, say, France or Belgium. The larger question we need to ask is whether the governments - and ultimately the inhabitants - of the democracies have the commitment and the willpower to follow where Israel leads. And this in turn raises an even larger question. To what lengths can and should a liberal democracy go in defence of its own values?

Security analysts agree that the Belgian authorities were dangerously slow off the mark. Known suspects were not investigated thoroughly enough. Intelligence that reached one arm of the Belgian security apparatus appears not to have been shared.

The fact is that, for some considerable time, Belgian police have been fearful of entering Islamist enclaves in the capital, such as Molenbeck, which was allowed to become a haven for armed Muslim gangs and bloodthirsty Muslim preachers.

Such enclaves thus became fertile recruiting grounds for the Islamic State. Belgian-born Islamists were shipped to Syria and Iraq for training and have now returned to carry jihad into the cities of western Europe, taking their EU passports with them.

But prevention is always better than cure. In order to gather the necessary intelligence that will forewarn us of further attacks, our security agencies need to penetrate the sophisticated networks that the terrorists have established. This means that agents must be recruited to work inside these networks and that private communications must be intercepted. And such measures as these mean, in turn, that some of the values we hold dear will have to be compromised (as they were in this country during the Second World War) while the emergency exists.

Speaking at a press conference in the immediate aftermath of the terrorist outrages in Istanbul and Brussels, Israel's Prime Minister Bibi Netanyahu listed the specific measures that the Jewish state employs in combating the terrorist threat: "We enter neighbourhoods, villages, make arrests, demolish terrorists' homes, take away work permits, shut down inciting media channels… We've closed the main borders and are completing work on the fence to prevent access to Israel's cities."

I doubt that many western democracies would go so far as to demolish terrorists' homes. But research carried out into the mind-set of average Islamist suicide bombers suggests that the one fear that they have - and which might just possibly deter some of them - is of the consequences for their families after their murderous work.

In an ideal world, the innocent should not be punished for the sins of the guilty. But at the very least the deterrent effect of familial consequences needs exploring. EU taxpayers' money is used by the Palestinian Authority to reward and support the families of dead terrorists. This cannot be right.

On March 15, the official Islamic State mouthpiece Al-Naba declared, however, that the fight against Israel should not take precedence over global jihad. Islamic State is in no doubt that it is engaged in a world war. So it is. And so, therefore, are we.