Mike (Trux) in his old BEF establishment details lists three squadrons of three troops, each with two motorcycles and three armoured cars. I assume that you don't have a copy ?
Hi Nick Leo Neihorster has a detailed breakdown of the War Establishment organisation that 12th Lancers used in 1940 over at his very useful website here: http://www.niehorster.org/017_britain/40_org/non-div/armd-car-rgt.html which agrees with the organisation Rich outlined above. Cheers Peter