EVERYBODY knows the EU is a trading bloc. Not everyone realises that secrets are among the commodities it trades in. 

True, 60 years after the Treaty of Rome there is still far from a single and free common market for intelligence across our continent in the way there is for butter, flights or financial services. 

But, slowly and haltingly, the 28 member states and one or two of their closest and most intimate allies are starting to exchange confidential information. 

READ MORE: Beyond Brexit: Brexit poses threat to countries working together on law and order, says General Secretary of the Scottish Police Federation

Some of it is potentially life-saving.

That is because trust, between nations who often fought on different sides in two world wars and a cold war, is gradually growing. 

All of Europe now faces a common threat from Salafi Jihadist terrorism, those inspired by or led by the so-called Islamic State. 

Some Brexiters have claimed that perceived shortfalls of intelligence – especially the failure to prevent high-profile atrocities in France and Belgium – suggest the UK has little to lose from edging back from this embryonic spirit of secret-sharing. 

Sir Richard Dearlove, the former head of MI6, before the June vote, downplayed any disruption to joint action. He said: “The truth about Brexit from a national security perspective is that the cost to Britain would be low.”

Other law enforcers and politicians take the opposite view: that the Paris, Nice and Brussels attacks underlined the need for Europe to share information more, not less.

And Sir Richard – basically the equivalent of a retired “M” from James Bond movies – was, of course, talking before America elected isolationist Donald Trump as president. Mr Trump is far less alarmed by recent Russian posturing than most European leaders and – alarmingly, according to critics – appears to believe there is a quick fix to Islamic State.

There has been much discussion on what will happen to cross-border cooperation between police and prosecutors after Brexit. Law enforcement insiders hope and expect the UK to try to find some way to continue to work with – if not in – Europol and Eurojust. This, of course, will likely come at a price. 

There is an issue, however, with mood music. How generous is Britain in sharing the intelligence it gains from the “Five Eyes”? This is the data that comes from the security services of the white anglophone world: the US, New Zealand, Canada, Australia and the UK.

Sometimes such information is shared through formal and informal networks, such as the Club de Berne, the gathering that brings together intelligence chiefs from EU states, Norway and Switzerland.

Will this change after Brexit as wider ties between the UK and the continent loosen, or are perceived to loosen?  What about the European Counter-Terrorism co-ordinator? Will Britain still be able to access this? 

And where does Scotland, with its own legal jurisdiction and distinct policing, come in to any changes in what policy wonks call intelligence and policing architecture? Scottish law enforcement figures have been keen to stress their openness to co-operation, in contrast to what some in Europe perceive as English reluctance to do so.

READ MORE: Beyond Brexit: Brexit poses threat to countries working together on law and order, says General Secretary of the Scottish Police Federation

Some Scots openly talk about having to play go-between for continental colleagues who cannot quite get an English colleague on the phone.

Could Scotland, inside or outside the UK, end up acting as an intermediary between Europe and England?

Or might such an arrangement end up being just another EU secret no one speaks of?