I have given this lamp the number LT3 because the guy I got it from told me it had been his fathers lamp which he had been issued with by London Transport. So far this is the only example I know of. I am sure the guy was telling me the truth but I would very much like to see one or two more to convince me it was not a one off creation.
I've seen two on eBay in the past few years. The first I didn't bid on because I didn't recognise it for what it was - I found out a couple of months later. I thought someone had just stuck an old electric fire reflector onto the back of their X246B. The second I did bid on but in the end it went for something stupid - far more than I was prepared to pay at the time for a pimped-up X246B. I've regretted it slightly ever since. One day, maybe - unless you'd care to flog me yours, Neil..?