Being head of Mossad? It's a lonely job

This anti-ideological instinct apparently prepared him well for the decision-making process at the helm of Israel's national security agency. He says: "Each issue must be decided on its own merits and also on the immediate circumstances prevailing at that moment. That makes it difficult because you cannot always go to precedents. Often you could not go back to past precedents but instead forge conditions of the moment."

When you adopt a political approach to a professional problem, you pay a price

Mr Halevy was in the UK on a speaking tour on behalf of Gesher, an NGO which aims to promote social and political unity in Israel. Discordance among decision-makers is evidently an issue close to his heart: while head of Mossad from 1998-2002, he served three prime ministers, Benjamin Netanyahu, Ehud Barak and Ariel Sharon. All were famously difficult characters in their own ways, and Mr Halevy points to the complexities involved in reconciling the demands of political leaders with national security requirements and the needs of the intelligence service: "You have to be able to serve your master, protect your master and protect the service you are heading."

With the only hint of emotion displayed throughout the interview, he adds, with a smile: "And sometimes this becomes a complex to deal with… it is a very lonely job."

Mossad evolved into a legendary outfit during Mr Halevy's 28-year stint in the agency, its operations so successful that it became stock material for conspiracy theories the world over.

For those who understand intelligence-gathering, however, one of the core reasons for its success was no secret: its capacity to marshal and collect human intelligence of the highest quality.

Mr Halevy explains that Mossad's human intelligence capabilities were forged in the cauldron of multiple, simultaneous conflict. Israel has learned that in order to be successful, it had to treat its enemies as separate entities. "The way you deal with Hamas is not the way you deal with the Palestinian Authority, which is not the way you deal with Hizbollah," he says.

Mr Halevy, however, believes that the Israel of today is not utilising this insight.

"For his own reasons, Netanyahu is conflating all the shades of terror into one large mass. This is counterproductive on an operational level. To deal with Hamas, you have to deal with Hamas per se. It's professionally wrong. When you adopt a political approach to a professional problem you pay a price for that."

Mr Halevy has been openly critical of the direction being taken by the Israeli government on several occasions, and suggests that on terrorism, current policymakers are insufficiently "accurate and circumspect", and need to be "more attuned" to the exact matter they are dealing with.

He will not, however, hand out lessons to other intelligence agencies. Despite the widespread criticism of Belgium's security forces for allowing the Brussels suburb of Molenbeek to become a hub for jihadist activity, he says: "It is improper for me - I am no longer in office - to judge my successors, but also improper from point of view of the information that they have at their disposal… More you get to the top, the more the issue of terrorism becomes part of a wider panorama of issues. So it's not for me to pass judgment."

In other statements however, Mr Halevy has hinted at a degree of misguidedness in the way European policymakers have dealt with their Muslim minorities, pointing to the French ban on the burka.

One wonders, therefore, how he thinks Europe should deal with the wider problem of extremism given that Brussels terror attacks were celebrated by several Muslim groups, and one of the perpetrators Paris atrocities, Salah Abdeslam, managed to hide out in Molenbeek for several months undetected.

He says: "You have to differentiate between the two strata of terrorism - those who are trained and motivated to carry out terrorist acts and a larger backdrop of sympathisers. I don't condone this [celebration of terror] at all - no way. But in order to be professional, you have to differentiate between the two. You have to devote efforts to both.

"Terrorists are not one large mass of people who have the same background, the same religious precepts, one single goal. There are different schools and aims. There is national terrorism and other global groups such as Isis and Al Qaeda. Hamas does not have global aspirations, even if they are members of the Muslim Brotherhood."

He does, however, indicate that European security and social policy has not been not sufficiently "honed to specifics", or joined-up enough. "We need a much greater degree of co-operation, even to the level of policies. The way you treat the Muslims is only a national policy at the moment - there is no EU-wide policy. This needs to be revisited. The Paris attackers went to Molenbeek. The 9/11 attackers spent years in Hamburg."

It does seem odd that the issue of security jurisdiction is being held up by the former head of an organisation that earned a reputation for taking out terrorists wherever they are in the world.

Mr Halevy insists, however, that "we always did our best to keep the law and act within its confines", but hints that the establishment of a set of international espionage rules might not be a bad thing.

"There has been a lot of codification of the laws of war. There has never been a codification of the rules of espionage. No service in the world is working within the confines of a detailed set of legislation which says what is permissible. This is important to realise. This makes life more difficult for those involved in espionage. You have to then make a deep effort to realise what is ethical, what is acceptable, what is understandable, what can be done."

How, then, does the lonely operator assess his shift defending one of the most threatened countries in the world? "We in Israel have conducted ourselves with a lot of wisdom," he says.