At an EU summit in Brussels, the prime minister urged leaders to consider “the safety of your citizens and mine”.
She called on them to give negotiators a new mandate to achieve the “crucial objective” of a comprehensive security agreement, amid EU officials intransigence on allowing the UK to participate in the bloc’s law enforcement programmes as a “third country” after March next year.
Over a working dinner on Thursday night, Mrs May warned, if the UK was blocked from involvement in key initiatives, that “we would no longer be able to share real-time alerts for wanted persons, including serious criminals”.
“Our collective ability to map terrorist networks across Europe and bring those responsible to justice would be reduced,” the prime minister added.
“That is not what I want and I do not believe it is what you want either.”
The EU’s chief Brexit negotiator Michel Barnier immediately hit back that an agreement must be based on the bloc’s “values and our principles” while also respecting the UK red lines, such as ending the jurisdiction of EU judges over Britain.
He also warned “time is very short” to conclude a Brexit deal and that a “huge and serious” gap remains between the EU and UK, in particular on the Irish border issue.
Mrs May wants Brussels to allow the UK to remain in programmes such as the Prum mechanism for sharing DNA profiles, the Second Generation Schengen Information System (SIS II) database of “real time” alerts about individuals interest to EU law enforcement and the European Criminal Records Information System (ECRIS).
However, the prime minister’s red line on accepting the jurisdiction of the European Court of Justice after Brexit has proved a stumbling bloc to the UK’s continued participation in such security initiatives.
Mrs May’s appeal to EU leaders went over the head of European Commission officials, who are leading Brexit negotiations and are said to be taking a tougher line on future security cooperation than member states might.
A senior UK source said: “The prime minister has given a firm commitment to the future security of Europe in the face of the severe threat from terrorists and malign state actors but to date European negotiators have put obstacles in the way of reaching agreement on mapping the movement of terrorists and criminals and sharing vital information.”
The prime minister later called for Brexit talks to “accelerate and intensify” as she left an EU summit dominated by the migration crisis.
Although it appeared talks on how to tackle the issue had hit an impasse on Thursday, with Italy reportedly the cause of the deadlock, leaders finally reached an agreement in the early hours of Friday.
Mrs May briefly addressed Brexit prior to the discussions on migration, with the EU27 to discuss their stance on the UK’s exit – in the prime minister’s absence – when they reconvene later on Friday.
The prime minister will seek to reach a consensus among her divided cabinet colleagues before the publication of a white paper setting out the government’s detailed plans for a future UK-EU deal on 9 July.
“We are going to be publishing our white paper shortly and I want to see the negotiations accelerating and intensifying thereafter,” Mrs May said in Brussels on Friday, shortly after 5am.
Yet, the prime minister had come under pressure to speed up her decision on what she wants in Brexit talks.
Irish prime minister Leo Varadkar told Sky News that Brussels, and Dublin, were fed up with waiting.
“We actually need to see the white paper from the British government as to what they believe the relationship should be like,” he said.
“And it is frustrating two years after the referendum that we still don’t have a white paper from the UK government as to what they think the relationship should look like.”
European Commission president Jean-Claude Juncker said: “I don’t have to lecture Theresa May, but I would like our British friends to make clear their positions.”
And Dutch prime minister Mark Rutte warned: “I am not losing patience but time is getting shorter and shorter to come to an agreement.”
Mr Barnier expressed hope the UK government’s white paper would include “workable and realistic proposals”.
Arriving before he briefed EU27 leaders at the European Council summit on Friday, the official said: “We have made progress but huge and serious divergence remains, in particular on Ireland and Northern Ireland.
“After Brexit the EU wants an EU-UK ambitious partnership, on trade as well as on security. But we have to base this partnership on our values and our principles, respecting also the UK red lines.”