Does "National Speed Limit" mean anything?

Today I returned home to Shropshire from Sheffield, using good roads but all 'A' roads.

I didn't start counting how many variations there were to the rule "30 m.p.h in towns, 60 m.p.h on single carriageway, 70 m.p.h. dual carriageways and motorways.

In fact I saw every variation between 20 and 60 m.p.h, with bewildering changes. The standard on my journey was clearly 50, which required very regular signs to warn me, but there were intervals of 60 and also of 40, with no apparent difference in road conditions or danger.

It is frankly confusing, and hardly conducive to road safety when a driver spends much of his attention on looking out for unexpected signs. There were signs warning of cameras, although I saw only one on the whole journey, but each sign was a further one to distract from the road ahead.

Cynics are surely right to say that the object is to raise money for the government, and to pay for all the camera cars and fixed cameras. I would add that I suspect that there is a green motive behind trying to reduce speed, and also some control freakery. I can't otherwise explain the bewildering collection of signs I encountered.