In addition to the ground based UNIT forces which are mainly recruited from the British Army there is a special operations squadron of the RAF, 633 Squadron.
Based on a Squadron used in particular complicated and difficult operations in World War Two: http://en.wikipedia.org/wiki/633_Squadron . It was reinforced by staff from the Danny Boy flight that fought during OPERATION IRONSIDE. After the War it was commanded by Wing Commander Jacko Dashwood who ultimately expanded it to include the Intrusion Counter-Measures Group until Group operations were taken off the RAF and given first to the Army and then UNIT in the later 1960s.
Mid-1970s 633 Sqd Buccaneer633 Squadron consists of fighter, bomber and transport flights which defend UK Air Space against extra-terrestrial threats and supports UNIT ground operations against alien and superpowered opposition.
Noteable operations 633 Squadron supported UNIT against include OPERATION GREEN DEATH, OPERATION THINK TANK and OPERATION MOTHER EARTH.
(With apologies to: http://en.wikipedia.org/wiki/Ministry_of_Space http://en.wikipedia.org/wiki/Remembrance_of_the_Daleks http://en.wikipedia.org/wiki/Victory_of_the_Daleks http://en.wikipedia.org/wiki/The_Green_Death http://en.wikipedia.org/wiki/Robot_(Doctor_Who) http://en.wikipedia.org/wiki/The_Seeds_of_Doom )
Kehaar's Blog 
[…] with UNIT (like RAF bases are RAF ‘place name’) rather than naming them after battles or such. 633 Squadron is assigned as air support but frequently called to other (NATO) […]