K Branch MI5

Counter-espionage 1968-94, hostile states counterintelligence c.2020s.

K Branch is a division of MI5 responsible for hostile states counterintelligence.¹

An earlier iteration of K Branch was responsible for counter-espionage in the service's organisation from 1968. Prior to this time, this had been D Branch.² The re-organisation was carried out by Michael Hanley as head of counter-espionage. Peter Wright claimed that he persuaded Hanley and Martin Furnival Jones to include a formal mechanism for investigating penetration of the service.³ K branch was reincorporated into a new D Branch in the service's organisation of 1994.⁴ At some later point this work seems to have reverted once again to the K Branch designation.