Submit an FOI request asking to see the Traffic Regulation Order that covers it as the start and end points are pretty precise. The terminal signage should also be not less than 600mm in diameter and in most cases should have a pair, the signs (TSRGD diagram 670-30) do not require their own illumination under Schedule 17 unless the route is a principle or primary route.

Are Street lights present on this road? If yes then it is by default a 30 limit unless signs are present to the contrary. Google Maps is useful as you can view roads across a time line