Thanks Anaconda, it's A=Basic, soft top, pick up, hard top. I assume Basic refers to the cab which I think is common to all Defenders, and the options refer to the rear section which means mine could have been a soft top or pick up with a County top added later...
But at least it's not a 1970's Cortina which if memory serves could be supplied with so many options and varieties no one ever managed to work out how many combinations there were, but it was in the millions... not that they actually made all them all - but I digress.