British Prime Minister Theresa May urged her country's European Union partners on Saturday not to let "rigid institutional restrictions" get in the way of a wide-ranging post-Brexit security alliance, warning that there would be "damaging real-world consequences" if none can be agreed.
In a speech to the Munich Security Conference, May sought to reassure foreign and security policy leaders on Britain's future commitment to European security.
"Europe's security is our security - and that is why I've said, and I say again today, that the United Kingdom is unconditionally committed to maintaining it," she said.
The British government has already called for a wide-ranging security treaty with the EU to ensure that intelligence-sharing and law-enforcement cooperation continue after Brexit, scheduled for March 2019.
Such a deal would allow Britain to remain a member of the EU police body Europol and keep use of the European Arrest Warrant, which allows for the quick extradition of suspects.
But it has been unclear what legal framework would underpin such a treaty, because Britain says it will leave the jurisdiction of the European Court of Justice.
May said the challenge is to put together a "deep and special partnership" with the EU to retain and further cooperation.
"This cannot be a time when any of us allow competition between partners, rigid institutional restrictions or deep-seated ideology to inhibit our cooperation and jeopardize the security of our citizens," she said.
"We must do whatever is most practical and pragmatic in ensuring our collective security," she added.
May conceded that there's no existing security arrangement between the 28-nation EU and a non-member that reflects the full depth of the existing EU-UK relationship, but argued that there's precedent in "comprehensive strategic relationships" in fields such as trade and there's "no legal or operational reason" why such an accord couldn't be reached on security.
"However, if the priority in the negotiations becomes avoiding any kind of new cooperation with a country outside the EU, then this political doctrine and ideology will have damaging real-world consequences for the security of all our people," she said, including much more cumbersome extraditions and an end to data exchange through Europol.
She said that a new arrangement must respect both the sovereignty of the EU and UK, and Britain "will respect the remit of the European Court of Justice" when participating in EU agencies.
Conference organizer Wolfgang Ischinger remarked after May's speech that "things would be so much easier if you stayed" - drawing applause.
May quickly slapped down that idea. "We are leaving the European Union," she said to a quiet room. "There is no question of a second referendum or going back on that vote."
The head of the European Commission said the EU-British security alliance will continue after Brexit, but didn't say on what terms.
"I believe, since we are not at war with the UK and we do not want to take revenge on the UK for what the British people have decided, this security alliance, the security bridge between the UK and the EU will be maintained," Jean-Claude Juncker said as he took the same stage shortly after May. "We still need it."
Juncker said a future security relationship shouldn't be mixed up with other Brexit-related issues, arguing that they should be considered individually.