BRUSSELS (Reuters) - EU officials who began talks with Britain on Friday on security ties after Brexit will raise problems that diplomats say may mean cooperation against terrorism and crime will be weakened more than many expected.

Among indications that what seemed the least fraught bit of Brexit is proving trickier is a recent EU report, described to Reuters, which slams Britain’s lackadaisical use of a key EU travel and crime database - the so-called Schengen Information System (SIS). Brussels also frets that London cannot be trusted to respect the privacy of EU citizens’ data after Brexit.

While EU political leaders are as keen as British Prime Minister Theresa May on keeping the closest possible security ties between the continent and London, one of the world’s leading powers in intelligence and crime-fighting, officials have been turning up a host of legal and technical obstacles.

“This always looked to be the easy bit of Brexit, the no-brainer that everyone wanted to keep good security cooperation,” said a person familiar with Germany’s work on the matter. “But as we get into it, we’re finding more and more problems.”

EU rules on what could be shared with third countries are an obstacle and Britain’s refusal to subject itself to judicial oversight of the top EU court - the European Court of Justice - also presents a hurdle to sharing information.

“Because of that, the reality is we might slide back to a less significant EU-UK relationship with perhaps more being done bilaterally,” a senior EU official said.

The EU has found a new sense of purpose in coordinating security work, notably through its Europol police agency, in the wake of an immigration spike in 2015-16 and Islamic attacks on both sides of the English Channel.

But EU diplomats said a report on Britain’s use of the SIS had highlighted disappointment on the continent. The bloc has decided Britain has used the information from other EU states but often failed to provide enough of its own or act on security requests of its peers.

“NO POLICE FACEBOOK”

“The SIS is not just a police Facebook where we share interesting stuff. All the entries come with alerts and requests for action and the UK has not been doing a good enough job,” said an EU diplomat.

The SIS is a trove of police intelligence data, collating member states’ information on anything from dubious documents to stolen cars to wanted persons or missing objects.

Britain, due to leave the EU in less than a year, has never been part of the European area of control-free travel called the Schengen zone. While the EU praises it as a top achievement of European integration, Britain has preferred to maintain full control of its own borders and immigration.

In 2015, however, Britain was given access to the SIS, a crucial tool in cooperation between EU states on border security, fighting terrorism and organized crime.

“If this is how they behave as a member state, how can we trust their commitment to the closest possible security pact after Brexit,” another EU diplomat said, adding there was no deadline for the EU to decide on cutting Britain off.

The European Commission, negotiating Brexit on behalf of the other 27 states, raised the issue in a recent Brexit briefing for national diplomats. The Commission declined to comment on the matter to Reuters, saying the SIS report was classified.

Britain’s interior ministry, the Home Office, said it was in talks with the Commission after the EU made recommendations for improvement. It said it was “fully committed” to the SIS and added: “We need to continue and enhance the internal security cooperation that already exists within the EU after Brexit.”

Statistics show the SIS was accessed more than 5.1 billion times by member states in 2017, of which some 540 million were by Britain - the third top score. In terms of uploaded alerts, however, Britain ranks only 15th.

The Home Office said Britain placed 13,100 alerts on SIS in 2017 and responded to over 9,500 foreign alerts.

The EU has warned London not to use its security prowess as a trump card to win concessions in other fields trade or expatriate rights. Both Britain and the EU say they want to foster a strong security partnership after Brexit.