Hi,
The guidance at CA23153 states:
The car is ‘unused and not second hand’, and is first registered on or after 17 April 2002.
New cars are ‘unused and not second hand’. You should accept a car is unused and not second hand even if it has been driven a limited number of miles for the purposes of testing, delivery, test driven by a potential purchaser, or used as a demonstration car.
The fact that such cars (or cars that have not been driven at all) may have been pre-registered to a dealer does not prevent you from treating them as 'unused and not second hand.
CA23153 - Plant and Machinery Allowance (PMA): First Year Allowance (FYA): expenditure on cars with low carbon dioxide emissions
Thank you.