Just to reinforce PaulJ comment re the registration for the car. Check this out very carefully. What does the V5 say?
There is a points system for registering a kitcar based on what parts/donor car/ mixture of parts resulting in what registration type is applied. Basic description is.....
All new parts......new reg...typical for Caterham.
Donor car......you generate points and if enough you retain the donor reg.
Bits and pieces bought randomly....Q plate.
This wasthe set up about 9/10 years ago and possibly the same now.
