They are the modern version of the old motorway 'Middle Lane Owner's Club' or MLOC (Hemlock). Get it?
Local roads are now a mix of 20 MPH and 30 MPH speed limits. They are badly signposted and nobody knows which is which, so they go half way - 25 MPH. In 30 limits they do 25, which would get a fail on a driving test for not making progress. Then in 20 limits they do 25, which is speeding and breaks the law. Both are wrong.
The problem is that councils are using by-laws to reduce the national urban speed limit by piecemeal. If it was government policy it would require an act of parliament.
So make it so. Pass an act that the new urban limit is 25 MPH and have done with it. Get rid of the 20 limits and all the speed bumps, speed cushions, sleeping policemen, rumble strips, chicanes and smiley / frowny signs and sort it out.