What sources dish out speeding tickets?

[Para J]

Drove the same way today, 30 signs and road paint, round the corner and small 20 and on road.....still my fault but still peeved. 30 limit had been ok for decades, parked cars in centre has always kept speeds to less than 20! Still peeved

I thought that to inforce a speed limit the correct size round warning sign must be displayed then they can be backed up with repeater warnings on the road and smaller repeater signs on posts.