FYI from Wikipedia:
There is no fixed definition of a classic car. Two taxation issues do impact however, leading to some people using them as cutoff dates. All cars built before January 1, 1973, are exempted from paying the annual road tax
vehicle excise duty. This is then entered on the license disc displayed on the windscreen as "historic vehicle" (if a car built before this date has been first registered in 1973 or later, then its build date would have to be verified by a recognized body such as British Motor Heritage Foundation to claim tax free status). The HM Revenue & Customs define a classic car for company taxation purposes as being over 15 years old and having a value in excess of £15,000.