The UK faces the risk of "serious disruption" to security co-operation with its European neighbours unless it moves swiftly to secure a post-Brexit deal, a new report has warned.
Prime Minister Theresa May has left no doubt of her desire to maintain close security links with the remaining EU countries.
She called in her landmark Florence speech for a "bold new strategic agreement" that replicates "the full scale and depth" of current collaboration on security, law enforcement and criminal justice.
But the report from the UK in a Changing Europe think tank warned that negotiations to reach a deal of this kind will be "hugely time-consuming" and cannot be left to the last minute.
The new report identified potential areas of difficulty including:
:: Data-sharing, where the UK may lose access to EU databases if it pursues the bulk retention of communications data - which is opposed by the European Court of Justice - and may even have to accept EU scrutiny of its security services;
:: Involvement with Europol, which will require an "unprecedented" deal if the UK is to retain access to databases and a participating place on the management board; and
:: The European Arrest Warrant, where the UK may need to secure a deal similar to the one which took Norway and Iceland years to negotiate and which would still prevent some EU countries from surrendering their nationals for trial in Britain.
The think tank's director, Professor Anand Menon of King's College London, said: "The UK and the EU have a clear incentive to continue to co-operate over law enforcement and counter-terrorism, given the obvious threats confronting them.
"Both sides have made it clear that they want a close relationship in this area in future.
"But this is fiendishly complex. When negotiations are likely to involve constitutional issues, disagreements over the role of the European Court of Justice and trade-offs from both sides, good intentions are not enough.
"Despite a shared desire to co-operate closely in future, nothing can be taken for granted.
"There is a danger that, unless the British Government acts quickly to define more clearly what it wants and how it might achieve it, another Brexit cliff edge - in security - might be on the horizon."