Read more: Brexit won’t mean Scottish independence

Read more: Brexit would hinder the fight against terrorism

Whether one is an enthusiastic European or not, the truth about Brexit from a national security perspective is that the cost to Britain would be low. Brexit would bring two potentially important security gains: the ability to dump the European Convention on Human Rights—remember the difficulty of extraditing the extremist Abu Hamza of the Finsbury Park Mosque—and, more importantly, greater control over immigration from the European Union.

One loss that would result from Brexit and which has been cited by Theresa May, the Home Secretary, as a reason for her supporting Britain’s continued membership of the EU, would be the European arrest warrant. But its importance has been exclusively criminal and few would notice its passing.

Britain is Europe’s leader in intelligence and security matters and gives much more than it gets in return. It is difficult to imagine any of the other EU members ending the relationships they already enjoy with the UK. Furthermore, counter-terrorist and counter-espionage liaison between democratic allies is driven as much by moral considerations as by political ones. If a security source in Germany learns that a terrorist attack is being planned in London, the Bundesamt für Verfassungsschutz, Germany’s domestic intelligence service, is certainly not going to withhold the intelligence from MI5 simply because the UK is not an EU member.

In addition, though the UK participates in various European and Brussels-based security bodies, they are of little consequence: the Club de Berne, made up of European Security Services; the Club de Madrid, made up of European Intelligence Services; Europol; and the Situation Centre in the European Commission are generally speaking little more than forums for the exchange of analysis and views.

With the exception of Europol, these bodies have no operational capacity and with 28 members of vastly varying levels of professionalism in intelligence and security, the convoy must accommodate the slowest and leakiest of the ships of state.

The larger powers cannot put their best intelligence material into such colanders. The British voice is nonetheless very influential because its intelligence and security community is, and will certainly remain, the strongest and most mature in Europe. Washington also appreciates that its closest ally enjoys this special European status at a time when the global threat from extremist terrorism remains at the top of most nations’ national security priorities.

The crucial practical business of counter-terrorism and counter-espionage is conducted, even in Europe, through bilateral and very occasionally trilateral relationships. Brussels has little or nothing to do with them, in large part due to what is known as the “Third Party Rule,” a notion that is little understood outside the intelligence fraternity but which is essential to intelligence liaison worldwide.

This rule states that the recipient of intelligence from one nation cannot pass it on to a third without the originator’s agreement. If an intelligence service breaks this rule it becomes a pariah. Politicians who loosely talk about intelligence sharing seldom seem to understand that this principle is crucial for the protection of sources and is one of the keystones of trust on which successful security partnerships are built.

European defence and security policy has proved to be little more than an aspiration. A European Rapid Reaction Force has not matured into an effective expression of Europe’s aggregated military power. Britain’s defence interests remain firmly hitched to Nato and a number of strong bilateral relationships, with France as our most important continental partner.

The inability of the EU member states to act together to stem the flow of migrants and refugees from the Middle East and Africa shows very clearly that, when essential interests are thought to be threatened, the national security considerations of each nation outweigh the principles of the European Charter of Fundamental Rights, on which the EU’s policy towards the problem is ultimately based.

Would Brexit damage our defence and intelligence relationship with the United States, which outweighs anything European by many factors of 10? I conclude confidently that no, it would not. The replacement of Trident, the access to overhead satellite monitoring capabilities, the defence exchanges that are hidden from public view, the UK-US co-operation over signals intelligence, the Central Intelligence Agency/Secret Intelligence Service/Federal Bureau of Investigation/MI5 liaison and much more would continue as before.

There would be disapproval of Brexit in Washington, and some disappointment too, but the practical consideration of living in a dangerous world and depending on true friends would win out. In short, Europe would be the potential losers in national security. But if Brexit happened, the UK would almost certainly show the magnanimity not to make its European partners pay the cost.

Now read: Twelve things you need to know about Brexit