The head of MI5 will appeal to European leaders on Monday not to put at risk their “shared strength” by weakening security and intelligence sharing after Brexit.

In a speech to European security chiefs, Andrew Parker, MI5’s Director General, will tell them that continued cooperation has never been more crucial in the face of Russia’s “aggressive and pernicious actions”.

Mr Parker’s intervention made pointedly in Berlin – the first time a serving head of MI5 has given a public speech on foreign soil – comes at a critical time in Brexit negotiations.