This appears to be an English law issue. Welsh and Scottish law are the same in this respect.

Well, if you go to the Patent office website and plug that number in (I cut and pasted, no chance of error) it says "publication number invalid".

Of course, if it is a patent, then copyright is irrelevant, and a patent owner would probably know the difference.

If a threat of patent action is made, then the person threatened may start a so-called "threats action" against the person threatening, so informed patent owners hardly ever write like this. They write "May I draw your attention to patent specification (number) a copy of which is enclosed".

So on balance I think you ought to write to this guy and say

"I am concerned by your email. I have checked at the Patent Office and find no patent of that number in force. May I trouble you for a copy of the specification? May I also draw your attention to Section 70 of the Patents Act 1977 as amended by Section 12 of the Patents Act 2004 and invite your comment? I should of course value your full and correct address shoud it transpire that I might have a cause of action under those sections. The chord wheel has of course been well known and publicised for many, many years, certainly prior to 1995."