The new chief of MI6, Blaise Metreweli, will warn of "the acute threat posed by Russia" when she makes her first public speech later.
She will highlight so-called hybrid warfare, which includes incidents such as cyber attacks and drones suspected of being launched near critical infrastructure by Russian proxies.
Ms Metreweli will describe this as "an acute threat posed by an aggressive, expansionist and revisionist Russia".
Referring to the war in Ukraine, she will insist that Britain will be keeping up the pressure on President Vladimir Putin on Ukraine's behalf.
