Are the Bettons no longer involved with Mercian? The last correspondence I had with them was with Bill Betton, son of D.W. who had passed on in the early 90's. We had a nice chat about a cycling holiday in New Zealand he had returned from. I assume Derek is Derek Land, who has been a long time builder with Mercian. I was able to visit the showroom in Alvaston in 1990, but not the Pontefract street works. Quite a sight, all the colorful Mercian frames and cycles(tandems,too)!
Best regards,
Wes Gadd
Unionville,CT