Citizens could be less safe if the UK has to leave key policing agreements after Brexit, Prime Minister Theresa May has warned EU leaders.
The UK says EU negotiators are blocking agreement on tracking terrorists and sharing information after March 2019.
The EU says once the UK becomes a “third country” it cannot have the same access to policing initiatives.
Mrs May urged EU leaders to “consider what is in the best interests of the safety of your citizens and mine.”
Speaking at a dinner in Brussels the prime minister said obstructing UK participation in law enforcement schemes would mean their ability to fight terrorism would be reduced.
“We would no longer be able to share real-time alerts for wanted persons, including serious criminals,” she said.
“We would be able to respond less swiftly to alerts for missing people on either side of the Channel and reunite them with their loved ones.
“Our collective ability to map terrorist networks across Europe and bring those responsible to justice would be reduced.
“That is not what I want and I do not believe it is what you want either,” the prime minister said.
She said EU leaders should tell their negotiators to allow the UK to continue to take part in schemes like the Prum mechanism for sharing DNA profiles, the Second Generation Schengen Information System – a database of “real time” alerts about certain individuals – and the European Criminal Records Information System.
She urged them to “consider what is in the best interests of the safety of your citizens and mine and give your negotiators a mandate that will allow us to achieve this crucial objective.”
BBC political editor Laura Kuenssberg said Mrs May hoped to persuade the 27 other EU leaders to move away from what the UK government regards as a rigid approach from the EU Commission in negotiations and to ease up on their “red lines”.
Earlier this month EU chief Brexit negotiator Michel Barnier said the UK would be kicked out of the European Arrest Warrant deal after Brexit – which allows EU members to request the arrest and detention of criminals in other countries without extradition talks between them. He argued it could not remain a part of it because the UK wanted to leave the European Court of Justice and free movement rules.
The prime minister has been briefing EU leaders at a summit for the last time before October, when both sides hope a deal will be done on the UK’s March 2019 departure.
But the European Commission president suggested UK cabinet splits were making things more difficult.
Arriving at the summit in Brussels, Jean-Claude Juncker said: “I don’t have to lecture Theresa May, but I would like our British friends to make clear their position.
“We cannot go on to live with a split cabinet. They have to say what they want and we will respond to that.”
The prime minister, who has been under pressure within her own party, has called her cabinet together for a meeting at Chequers on 6 July to agree the UK’s blueprint for its future relations with the EU.
Arriving in Brussels, Mrs May said she was looking forward to “securing our strong future partnership” which she said was in the interests of both the EU and UK .
“I think both sides are keen to continue that work at a faster pace than we have done up till now and certainly we would welcome that.”
The prime minister held a number of face-to-face meetings with European counterparts on day one of the two-day summit, which is focused on the migration challenges facing Europe and eurozone reform.
After 10 hours of talks which lasted into the early hours of Friday EU leaders said they had reached an agreement on migration.
The leaders said that new migrant centres could be set up in EU countries on a “voluntary” basis.
Mrs May welcomed the “positive conclusions” reached.
She said much of the agreement was “around what the UK has been encouraging for some time, which is taking more action upstream in countries of origin so that we can ensure that people aren’t having to make and aren’t making these very dangerous journeys.”
The remaining 27 EU leaders are due to discuss Brexit on their own on Friday morning, by which point Mrs May is expected to have left Brussels.