Most 20mph roads are now set as limits without physical calming. However "zones" only require a single physical calming device, so many legacy small zones are being expanded without further physical calming on additional roads. Its further confused by media not knowing the subtle differences.

Agreed. I would far prefer m/sec. So much better at describing speed than mph or even km/h.

There is plenty of evidence that when set across wide areas and inclusive of faster roads then speeds and casualties reduce. See www.20splenty.org/big_speed_re...

Both 20mph zones and limits are enforceable.

Its not only road user's actions, it's also the actions of those managing the roads and keeping speed limits which limit the ability of road users to avoid collisions when "incidents" happen. That's why responsible politicians and officers are setting 20mph for most urban/village roads.