Dear Rod,
Sorry for not replying sooner but I’ve been preoccupied with other things. Thank you for your reply and informing me of the size of the speed limit sign. I would like to correct you though; the sign is probably 60 cm not 600 cm. That would be massive. I don’t think you read my comment properly. I said that the change in the regulations to allow only one 20 mph sign whereas for all other speed limits, two are required, is not helpful because people driving in an unfamiliar town centre have more chance of missing the single sign because of all the other distractions.

You also said that to play safe one should drive at 20 mph if unsure of the speed limit. This is not helpful. It is quite frustrating to get stuck behind a vehicle that is going too slow without just cause as witnessed by myself some evenings on a quiet stretch of road in my home town of Wickford in Essex, where the limit is 40 mph. This feels like quite a sensible speed considering the gentle bends and its location just outside a 30 mph limit. If I happen to be following another vehicle, more often than not, when approaching the speed camera their speed drops to 30. This is despite the two large 40 mph signs at the start of the road and also the numerous repeaters on the lamp posts. You said that there is no reason why an aware driver would not notice such a sign. The fact is, more drivers than you might imagine are less aware than they should be. Also, not having repeaters is a bad idea. If the authorities have decided that for all other speed limits, two signs are required and repeaters at regular intervals on lit roads, apart from 30 mph limits, then I cannot understand why 20 mph limits should have different rules.
Correct me if I’m wrong but I understand that the original idea of 20 mph limits was to save lives of pedestrians who might wander into the dangerous road without looking.
As the article implies, cost is the driving factor here, not the safety of pedestrians.