Clearing House does not appear on any official EU listings of "working groups" - standard meetings of mid-ranking EU diplomats, which pre-agree EU decisions before they are adopted by EU ambassadors and, later down the line, rubber-stamped by EU ministers.

The group's main job is to decide, every six months or so, who should be on the EU's terrorist register and have their financial assets frozen, with the group meeting sometime this week to finalise contents of the next terror list before its formal adoption in early July.

Clearing House's internal decision-making is not open to any political scrutiny: when the secret service delegates write a new list of names, it is passed - without any accompanying evidence or reasoning - to a meeting of EU ambassadors, who automatically adopt it as an "A point" (an agenda item with no discussion).

The terrorist register hit the headlines last winter, when Iran opposition group PMOI claimed EU states are in violation of an EU court ruling to take it off the list. The court ruling found fault with lack of evidence and right to appeal on the original PMOI decision.

Following the verdict, EU states sent "statements of reasoning" to all the entities on the register, but in the case of PMOI the "statement" dealt only with pre-2001 activity. When challenged, EU officials said that "other documents" exist but cannot be revealed for security reasons.

The case is causing controversy in Denmark, where foreign minister Per Stig Moller will this Friday again be dragged in for parliamentary questions on whether Clearing House is open to manipulation: PMOI says there is no secret evidence and that the UK is using the EU terror brand to barter with Tehran.

The Danish idea

A May resolution signed by a majority of Danish MPs in the European affairs committee suggests there "should be made an independent body that can somehow control Clearing House and handle complaints [arising from people or groups who feel they have been unfairly treated]."

The resolution is set to politically dog Mr Moller but it does not legally oblige him to do anything. When asked by EUobserver if he might suggest the oversight committee idea to other EU foreign ministers meeting in Luxembourg on Sunday, his spokesman said "I doubt that very much."

"Unofficially, I've heard that all the other 26 member states are against this idea of an independent body," a Danish parliamentary official said. "But this kind of resolution is not normal - it only happens once or twice a year. I don't think it will go away so easily."

Meanwhile, away from the PMOI case or the radical Danish "oversight" idea, the German EU presidency is quietly working on a set of Clearing House reform proposals that was originally put on paper by the Finnish EU presidency last year.

Some of the ideas on the table include: forcing Clearing House to give EU ambassadors more information; making limited parts of the group's internal deliberations public and creating a new code of conduct for Clearing House delegates.

The open-ended reform process is not working to any deadline, but could see a flurry of activity when the new terrorist list is published in July. "I believe there will be some progress on transparency and due process. It's not just the Danes who want more transparency. But it can never be fully open," an EU official said.

Spy city

In general, when it comes to Brussels information security, a culture of tactical leaks by EU states who feel they are not being listened to behind closed doors often brings to light sensitive information, such as draft conflict resolution plans debated by the Political and Security Committee.

The most highly-guarded information is on operational details of EU police or peacekeeping missions in places such as the Western Balkans or Congo, with Brussels involved in triggering actions such as dawn raids on the hideouts of war crimes fugitives in Bosnia.

But EU diplomats have a sense of humour when it comes to Brussels' ability to control information, at the same time as sharing it between 27 member states, various European Commission departments and EU embassies around the world.

"How many spies are there in Brussels?" one EU diplomat asked rhetorically. "It's hard to say - how many diplomats are there in the American and Russian embassies?"

"After Washington, Brussels is the number two city in the world for spies. But they are either young ones or old ones because the information is so easy to get, you have to be either in training or in retirement," another EU official quipped.