By Stephen Fidler 

British Prime Minister Theresa May has long said she wants Britain to have a "bespoke" agreement with the European Union after Brexit.

One area where she has the best hope of getting a tailor-made deal is over law enforcement and counterterrorism.

In a speech in Munich over the weekend, she laid out her case for a very close British relationship in internal security matters with the EU that no other non-EU country enjoys. If that doesn't happen, she suggested, both sides will be losers.

National cooperation among EU countries has intensified over the past 20 years. EU nations share unprecedented amounts of information through six databases covering criminal records, vehicle registration, DNA, passenger-name records and much else.

They have developed Europol, which runs a database and coordinates EU-wide operations dealing with serious crime and terrorism. They have launched programs such as the European Arrest Warrant, which speeds extradition within the EU, and the European Investigation Order that expedites cross-border sharing of information from criminal inquiries.

For the U.K., losing access to all this and other programs could have important consequences. In Europol, for example, EU member states -- except for Denmark, which opted out -- can directly access Europol's database. Non-EU countries, even those with strong ties to Europol such as the U.S., must specifically request information.

Leaving Europol, said Rob Wainwright, the British director of Europol, would result in a strategic loss because the U.K. would no longer be sitting at the decision makers' table. It would mean "a loss of visibility and instantaneous access" to the Europol database, he said in an interview in January.

A British government paper published in September pointed out that "real-time or very rapid responses" to database requests "make a significant difference to the value of the information to operational partners."

The European Arrest Warrant speeds extradition based on mutual recognition of judicial procedures in other member states, avoiding lengthy litigation. If the U.K. isn't part of that program, without it the U.K. would likely have to revert to a 1957 convention where applications are made through diplomatic channels and can be refused.

Each warrant is also transmitted as an alert through the largest security database in Europe: the Schengen Information System, of which the U.K. is part even though it is outside the Schengen passport-free travel zone. That means an extradition request doesn't have to be targeted at a specific country.

Mrs. May laid out why the EU might be interested in a special deal on security. She pointed out that for every person arrested on a European Arrest Warrant issued by the U.K., the U.K. arrests eight on warrants issued by other EU member states. Extradition otherwise could cost four times as much and take three times as long, she said.

The U.K. is one of the largest contributors of data, information and expertise to Europol. On the Schengen Information System, around a fifth of alerts related to missing persons, wanted criminals and suspected terrorists and the like are circulated by the U.K.

The prime minister made clear that the U.K. wants to be part of these structures, but typically didn't make clear how.

She said that when participating in EU agencies, the U.K. would respect "the remit of the European Court of Justice" -- a stance that could ease the way to close cooperation. But she added Britain's "unique status as a third country with our own sovereign legal order" would also need to be respected, which would complicate it by implying Britain's legal system could impinge on EU affairs.

No non-EU members have the kind of relationship that Mrs. May seems to be floating -- except in some special circumstances where non-EU members of the Schengen travel area, like Switzerland and Norway, are included. None has a seat at the decision-making table.

Sorting this out will require delving into huge amounts of detail. But Mrs. May's appeal puts the EU in a quandary. It has so far rejected the idea that the U.K. can "cherry pick" the bits of the EU it likes and ignore those it doesn't.

However, there is risk for EU governments in pushing Britain away from the EU in security matters that they don't run in trade and economic affairs: It could make their citizens less safe.

What if delayed exchanges of information allowed a deadly terrorist attack that would have been stopped if Britain had been inside the tent? Shouldn't citizen safety trump a theology that dictates the U.K. should have a less-attractive deal outside the EU than inside?

Yet if EU governments do allow cherry picking in law enforcement and counterterrorism, they risk creating a precedent for the bespoke deal on post-Brexit trade and economic relations that Mrs. May also says she wants and which up until now they have forcefully rejected.

Write to Stephen Fidler at stephen.fidler@wsj.com

(END) Dow Jones Newswires

February 22, 2018 14:57 ET (19:57 GMT)