I have picked up the idea here or on somewhere else on the web that the two letters before the numbers relate to the framebuilder. Looking at our tandems, two start LA followed by five or six digits. A recent posting on Facebook mentioned Lee Cooper as a possible builder for a 1999 Vittesse. Checking Lee Cooper's website I see that during the period he was building for Thorn his business was called LA Cycles so this would all seem to tie up nicely. Our 2004 Discovery has MM as the first two letters but I've no leads on who that means or the KA on a year 2000 or 2001 frame.
The numbers might be serial number within month and year but I can't get an oder that works with all the numbers we have seen.
Can anyone fill out the meaning of Thorn serial numbers for the bikes made in the UK?