I dont know why people still believe so much fucking shite about this.
The information is clearly available from the government website after seconds on google.
Keep a vehicle’s original registration number
A rebuilt vehicle can keep its original registration number if you can prove you’ve used:
the original unmodified chassis or bodyshell (car or light van)
a new chassis or monocoque bodyshell of the same specification as the original (car or light van)
the original unmodified frame (motorbike)
a new frame of the same specification as the original (motorbike)
You must also have 2 other major components from the original vehicle from the following lists.
For cars or light vans:
suspension (front and back)
steering assembly
axles (both)
transmission
engine
So with a brand new shell (and be prepared to prove its new), you keep the reg no. This used to be common place with new high value cars after a crash thats bent the chassis but not much else (eg side impact into pillar/sill).
Of note for all the cossie conversions and crazy conversions:
8. Radically altered vehicles
Your vehicle must comply with the road vehicles regulations if you use it on the road.
Radically altered vehicles are vehicles that have been altered from their original specification, but aren’t kit conversions.
DVLA uses a points system to decide what registration number to give a radically altered vehicle.
Keep the original registration number
Your vehicle must have 8 or more points from the table below if you want to keep the original registration number. 5 of these points must come from having the original or new and unmodified chassis, monocoque bodyshell or frame.
Part Points
Chassis, monocoque bodyshell (body and chassis as one unit) or frame - original or new and unmodified (direct from manufacturer) 5
Suspension (front and back) - original 2
Axles (both) - original 2
Transmission - original 2
Steering assembly - original 2
Engine - original 1
Another one that applies to rebuilt classics or cars built up from a shell and parts sourced elsewhere:
DVLA can only recognise your vehicle as a reconstructed classic vehicle if it meets certain criteria. It must be:
built from genuine period components from more than one vehicle, all over 25 years old and of the same specification as the original vehicle
a true reflection of the marque
The appropriate vehicle owners’ club for the vehicle type (‘marque’) must inspect the vehicle and confirm in writing that it:
has been inspected
is a true reflection of the marque
is comprised of genuine period components all over 25 years old
They must also give manufacture dates for the major components.
DVLA will assign an age-related registration number to the vehicle based on the youngest component used.
New or replica parts
Your vehicle won’t get an age-related registration number if it includes new or replica parts. DVLA will give your vehicle a ‘Q’ prefix registration number. Your vehicle must pass the relevant type approval test to get a ‘Q’ prefix registration number.
Thats the law, however what people get away with in practice is very different.
many cossie conversions would easily fall foul of the rules and end up on a q plate if not done carefully. Anything with a cossie floor grafted into another car is blatent q plate territory.