LONDON, Dec 15 - The head of Britain's Secret Intelligence Service, the foreign spy service known as MI6, will warn that Russia poses an "aggressive, expansionist, and revisionist" threat, in her first speech ‍since ​taking office.

Blaise Metreweli took over from Richard Moore in ‍October, becoming the first female chief of MI6 - a role publicly known by the codename "C" - in its 116-year ​history.