Been tracking these on FlightAware for a couple of years now and yeah, the pattern is weird. They pop up with almost no notice, usually mid-week, and the stated reason is almost always just "military operations" which tells you precisely nothing.
What gets me is the shape of some of them. Not just a standard radius circle around a known base, some of them are these odd elongated corridors that don't line up with anything on the public record. Had a similar thing happen over parts of Derbyshire a few years back actually, lasted about three days and nobody ever explained it locally.
Not saying its little green men but the lack of transparency is frustrating even from a purely practical standpoint for pilots. You'd think they'd at least have to file something more specific.
Anyone cross-referenced the dates these restrictions appear with any of the tremor data from the USGS? I did a rough comparison a while back and there might be something there but my sample size was too small to say anything definitive. Would be good if someone with more time could dig into it properly.