The head of MI6 has joined with his French and German counterparts to appeal for continued intelligence-sharing after Britain leaves the European Union.
In a rare joint statement, the three intelligence chiefs said co-operation between EU agencies was "indispensable" against a background of "diverse foreign and security policy challenges".
"Even after the UK's exit from the EU, close co-operation and cross-border information-sharing must be taken forward on themes such as international terrorism, illegal migration, proliferation and cyber attacks," they said in the statement posted on the German BND intelligence agency's website.
The call followed a meeting between MI6 chief Alex Younger, the head of the BND, Bruno Kahl, and the director general of the French DGSE, Bernard Emie, at the Munich Security Conference.
"The three service heads are united in the view that modern threats require a modern response, any failure to do so would lead to even greater risk," the statement said.
"To have effect, our efforts must be combined in partnership. The agencies are capable services; they make a powerful contribution.
"Co-operation between European intelligence agencies combined with the values of liberal democracy is indispensable, especially against a background of diverse foreign and security policy challenges."
Their intervention came as Theresa May was preparing to address the conference with a speech on Saturday, setting out her vision for future security co-operation with the EU after Britain leaves in March 2019.
Earlier, the former director of the GCHQ electronic eavesdropping agency, Robert Hannigan, urged the Prime Minister to "give some detail", warning she would "disappoint" her European audience if she simply restated her wish for a special security partnership.
"One of the things we will be withdrawing from are those mechanisms that influence European policy on sanctions and other areas of common security and defence policy," he told BBC Radio 4's Today programme.
"The Government has said it wants to be fully part of that conversation. It needs now to set out, what's the proposal for that? How are we going to interact with the EU in future on policy on defence and security?"