There's a couple of points about the new 20mph zones in Wales which I think may have been overlooked.
First, in all probability, your car's speedo is set at least 3mph LESS than actual [it can be a lot more], so if you're speedo says you are doing 30, you are doing 27 at most, pos less. Same with 20mph, you're doing 17mph MAX.

So this means that when Mr/Mrs cautious drive at 18/19mph in the new zones, they are doing 15/16 mph, possibly even less. Consequently it seems like a crawl, which it is. Obviously this stuff isn't really discussed in the media.

The Welsh Gov. are bringing in the Fire Brigade next month to stop motorists who are caught over 20mph. They'll be given the option of an on-site safety lecture or a fine/endorsement. Just to let folk know, if they say you were doing 24 mph in a 20 mph zone, tell fireman sam to f**k off. Because of the above, there is a tolerance level of 10% + 2 .

Happy motoring.