AKA Cambridge carrier

[David Herbert]

Pilot vehicles would normally have had civilian style registration numbers like UXM65. They also usually had a large P1, P2 etc in white painted on in obvious places for easy recognition. These were used for basic development of the design.
Pre production vehicles usually had army registrations like 60BA09 and a large W1, W2 etc. These were built for troop trials but often had major modifications as the trials went along.
Series production vehicles would have army numbers.
FVRDE / FVPE numbers were allocated to all individual vehicles being developed or tested by those organisations. They were painted on any obvious flatish surface, often on the front and were often refered to as 'wing numbers' as they would be painted on a front wing (fender) of a wheeled vehicle.

David