@chrisbeach - in a 20mph zone, you should be driving at, or less than 20mph. I know that you know that Lewisham is a 20mph borough. You have no excuse. Other drivers might not know that Lewisham is a 20mph zone, but there’s enough signage, and road markings to make it obvious - they also have no excuse.
in terms of GLA road (Transport For London Red Route/Road Network - TLRN) - they manage and maintain the red routes, and also the ‘red route related infrastructure’ on side roads - so this would only be signs, and road markings specifically related to the red route. So for instance a red route parking sign that has fallen over, 5m into a side road would be TfL responsibility to fix, whereas a pothole in the carriageway, 5m into a red route side road, would be, in this case, Lewisham Highways responsibility to fix.
whatever you might think, enforceable, or not, the TMO for 20mph across Lewisham will have been checked and double checked to ensure that it is legally accurate, and enforceable, and as I’ve said previously, if you have an accident and knock down a pedestrian, on a borough road/residential side road, and it’s proved that you were travelling more than 20mph (but less than 30), then trying to use the excuse that it’s perfectly ok as the TMO is not enforceable, will definitely not go in your favour.
There might be many things wrong with a blanket 20mph zone, it might encourage dangerous overtaking by other idiots, it might increase pollution due to vehicles being less efficient at lower speeds, and revving and braking harder, but it’s still a legal speed limit that should be adhered to like any other.
obviously it is “GLA roads and (GLA) side roads” rather than “GLA roads, and (other non GLA) side roads”