20 limits are the tip of the iceberg. In Wales (where else would it be?) either side of 20 limits is now 30 where it used to be 40.
One long local stretch of well maintained hazard free dual carriageway that is a significant arterial route has gone from 70 to 50 with no explanation. The only reasons I can see is that cyclist competing in a race was knocked off & died (who had the bright idea of holding a bicycle race on a dual carriageway?) Or its just a petty bureaucrat or politician with a personal axe to grind.
And there's a stretch of A road that has been reduced to 30 for several miles because its a tourist route and dozy tourists drive slowly holding up all the other traffic. Solution? Reduce the speed limit to suit the minority so they can admire the views without having to stop!