We can only hope that the signs are being removed in preparation for the introduction of the borough wide 20mph zone.

This thread alone clearly shows that currently drivers are not aware of isolated 20 mph areas - even people who live in the roads themselves.

It will take time, but as more boroughs sign up to the new speed limit, then most drivers will adjust. Residential roads = 20.

The problem is how you stop the 20% who will not comply and are more likely to be uninsured, untaxed, banned, over the limit and breaking the law in other ways.
You would have thought most drivers would want them off the road too, as these are the people more likely to cause accidents, but instead somehow see any enforcement as some massive infringement of drivers' freedom.