When the Vulcan moved from the high-level nuclear role to low level operations, it received "wrap around" camouflage, as it would be operating, for example, up valleys and flying low over various terrain features. Underside camouflage helped when the aircraft was turning and banking, as observers possibly could be at a higher level than the aircraft !
This camouflage style continued onto other strike aircraft, such as Buccaneer, Jaguar, Harrier and Tornado, until replaced by the current overall grey schemes.