A child's bicycle with stabilisers is still a bicycle, not a quadricycle, so I reckon a Mini Comtesse is a tricycle* with stabilisers. Now the authorities might not classify it as such, because buffle-headed bureaucratic dandiprats all over the world seem immune to Logic and Common Sense, but to me Stabilisers are not "normally" in contact with the road, and are therefore not "road" wheels. Plenty of vehicles are prevented from turning turtle by their own body work, if projecting bodywork on a MC or Peel happens to have a rotating component so much the better!
* OK, a THREE-WHEELED Tricycle, just to be clear!