Probably 30 years or more ago now walking the back street route from Paddington to the B.R.B. I passed a small, locked yard somewhere just before the Edgware Road, possibly underneath the Westway(???).
The striking feature was that it contained about 4 expensive cars and all had registrations of just the letter 'A' and a single digit (can't remember which, though)
Seemed very strange that they were in such a short sequence. Strange, too, that they didn't represent the usual motives for 'personal regs' unless to show that the owner had owned cars for a very long time, indeed from the first to be registered, which presumably the 'A' series were.