If anyone wants an idea of scale of problem with illegal/overpowered/derestricted Ebikes just search ebay (uk) for ebikes. There are more 3000w kits sold than 250's . You done find a legal kit until around 12th listing. There are around 600 listings for kits. At a guess I, d suggest 1 in 10 is legal.
Point many have been making for years now is that people are not riding pedelecs, legal Ebikes. In majority of cases they are on uninsured, untaxed, unregistered and MOT fail motor bikes.
For a long time this forum has supported such behaviour.
I hope chap was on a legal bike in this case. However, it's only a matter of time before something is done.