Martin Underwood wrote:
Adrian wrote in
70:

Endymion Ponsonby-Withermoor III ) gurgled happily,
sounding much like they were saying :

Repeater signs.
From the bottom of the speed limit table in HC103 - "The 30 mph limit
applies to all traffic on all roads in England and Wales (only Class
C and unclassified roads in Scotland) with street lighting unless
signs show otherwise)"

Basically, all speed limits except the default must have repeaters
every so often. If they aren't there, then the default applies,
regardless of the last "big" sign. That's 30 if there's streetlights,
NSL (60 S/C, 70 D/C) if there aren't. Motorways are default 70,
streetlights or not.

The difficulty is the definition of the term "street lighting": it means
that the lights are closer together than some cut-off distance (can't be
arsed to check the distance: my HC is in the car). As you are driving past
them, try judging whether the lights are closer than this distance (and so
the limit is 30 mph) or whether they are just further apart than this
distance (and hence the limit is 60). On a major road with more than one
lane you can easily think that 60/70 would be appropriate (or at least that
it's safe to drive at 40 or 50), even though there are houses some distance
away from the road, separated by service roads on either side.

If you are a on a road of that kind with a speed limit other than 30mph
there will be repeater signs at intervals (can't be bothered to look up
the guidance on the interval distance). If the speed limt on that road
then changes to 30mph there will be '30' signs at the point of change.