ok it looks as if SVA applies only to motorcycles and IVA (Individual vehicle approval) is what applies the intended car
(a heavy quadricycle category also exists but these are only allowed 15 kW)
3 wheels and unladen weight below 896 lb is/was in the UK a motor-tricycle ie a motorcycle not a car
(pre-1962 UK purchase (sales) tax was 45% for cars but c.20% for motorcycles and such motor tricycles)
3 or 4-wheeled the 'cyclecars' of 100 years ago are in fashion again - many are still active in motor sport
one nice man uses a 1908 5 litre V8 aero engine in his road-going GN
40-plus year old cars are now road-legal without annual inspection ('MOT') or annual license fee ('road tax') ....
some even without modernities like indicators, lights, seat belts, or roll protection ...
'jalopy-style' - but yes here in the UK