I would also point out that a UK patent cannot be valid if the invention was not novel (or within a convention priority period if first applied for in another country) at the time of application, so my first reaction is that even if Oglesby has a patent that we have not managed to discover (and I did that other search too with the same result), it is likely to be invalid, which would make his threat unlawful, and so make a threats action possible.

The UK has a pre-grant examination process for patents, and I would have expected an examiner to have thrown an application for this alleged patent out as not being novel.

However, there is no necessary registration process for UK copyrights (you can still effect registration at Stationers' Hall, but it achieves pretty well nothing). It is unlikely but possible that Oglesby has purported to register a copyright there and got this number (it does not look like an appropriate form of number). He might then have a valid copyright for his particular artistic work or work of artistic craftsmanship - which could be infringed by copying that particular work, but not by copying any other work (even if that other work was a chordwheel) unless that other work, of course, was a copy of Oglesby's work.

I still recommend writing to Oglesby. He may be genuine, but ill-informed, and a letter might get to the bottom of things which is better than risking litigation on assumptions. He is not a spammer as such, as there is no evidence of random distribution, and no evidence of intent to obtain commercial gain (yet), so what is the downside of writing?