Regarding the lack of signage, the Traffic Signs Manual published by the DfT says that 30mph ‘repeater’ signs are not allowed if there are street lights along the road. This makes sense because if there are street lights the speed limit is 30 unless signs say otherwise, and if you put them on one road you’d have to put them on all roads to be consistent.
However, it goes on to say the following about reducing a speed limit to 30 mph (paragraph 14.33):
“Regular drivers might not at first realise that the
speed limit has changed; they might not notice that
the speed limit signs have been removed. A sign to
diagram 7032 should therefore be erected to advise
drivers that a new 30mph speed limit is in force”
The key word is ‘should’ (paragraph 1.5):
“should indicates a course of
action that is strongly recommended and represents
good practice”