Just to add a bit more to this post, Will Curry is correct in that MG 7775 now belongs to an MG car.
What actually happened was that in October 1993 a very good friend of mine, whom I have known for many many years achieved his life’s ambition to own an early MG sports car. He bought a 1948 MG TC that had been restored from a wreck by another man who I also knew, and who had made a magnificent job of the restoration. However as the original registration number had been lost, he re-reregistered it in July 1989 with an age related number. He then drove the car until 1993, before selling it to my friend. The registration number on the car was TSU 673, which we both thought looked horrible and completely destroyed the character of the car, so after much persuading on his part I agreed with my friend in May 2000 that he could have my MG number for his car as long as he promised not to immediately sell either the car or the number plate on for a profit. Well that was twenty years ago and my friend still has the car and he still enjoys driving it so he was as good as his word.
We had to take both vehicles to the DVLA local office in Chelmsford to be inspected, which went off without a hitch, and my Ariel is now MSL 657. As I haven’t ridden the Ariel for over twenty years I haven’t bothered to change the plate, although I have the new plate and will fit it before I put the bike back on the road.
I didn’t mention this in my first post as that post was already too long, and I was really only asking about the frame number.
So to return to the original question, I was hoping that this post would give me a simple answer as to how my log book, with five figure numbers for both engine and frame numbers and with no prefixes on either came in to be in existence. What I was trying to avoid was a situation where either I, or more likely my son, would be hit with accusations of either fraud or vehicle theft if he wanted to sell the bike at some point in the future. Obviously there is no simple explanation to this otherwise it would have surfaced by now, but the log book is completely genuine so there must be an explanation, it's just that we haven’t found it yet.
I bought the log book and the frame in good faith in 1975, and I built the bike and put it on the road in 1981, and its been taxed and tested continuously until 2001, and there has never been a query about it. If there has ever been any skulduggery with either it must have taken place before they came into my possession, as I have owned both for the last forty five years.
So what to do now, fortunately I’m fit and well at the moment so I’ve got some years left to think about it.