Sorry Deano, thats not quite right, it has to be manufactured before 1.1.73 and also be registered before some date in the middle of january 1973 for it to work.
No Deano is right. My LR was built in 63, but not registered until 74 (MOD) and still qualifies. From the DVLA:
Vehicle registration Document/Certificate (V5/V5C) – This must clearly show a date of registration or manufacture of the vehicle prior to *1 January 1973. If the registration document/Certificate is not available or if you think the age shown is incorrect, you will need to produce a dating certificate from a vehicle
enthusiasts club or evidence from the vehicle manufacturer.
*Note: Where a registration document/Certificate indicates that the vehicle was registered up to and including 7 January 1973, we
are prepared to allow entry into the Historic Class on the basis that the vehicle would have been constructed the previous year.