In the early days, each 'local' licensing authority kept their own registration records (think county level, although some 'metropolitan' boroughs would have their own facility).
The creation of DVLC (now DVLA) at Swansea in 1965 'centralised' all records, although many vehicles that were untaxed at the time of the changeover were 'lost' to the system at the time that card log-books gave way to paper ones.
I doubt that any record of early vehicles is held anywhere (unless they have been in continuous 'use').
http://www.speedyreg.co.uk/history-of-number-plates