The director of the EU policing agency has warned Britain could be more vulnerable to terrorism and other forms of organised crime post-Brexit if negotiations over security don't achieve an effective solution.
Rob Wainwright, the British Director of Europol, insisted ministers had to get the details right.
He told Sky News: "I've seen how threats of terrorism and organised crime have become much more global.
"Therefore, the need for greater international police co-operation is absolutely essential to keeping us safe.
"It is important for Britain to get this right. It is about the security of the country - and not just the security of Britain, but of Europe."
He discussed the possibilities for the UK after the withdrawal - namely the country could become an associate member of Europol to grant access to the organisation's capabilities, if not the national database.
A government spokesman said this had always been a clear objective for Theresa May:
"As part of the negotiations, we will discuss with the EU and its member states how best to continue co-operation on security, law enforcement and criminal justice."