The correct size design and positioning of road signs is very clearly set out and any deviation from the regulations may result in the speed limit being unenforceable at law. If you are caught by a speed camera it is worth returning to the "scene of the crime" to check that the road signage is correct. See if the signs are badly faded or obscured or are the wrong size or colour. Take photos of the signs showing the whole road. If you suspect that the signs are not legal, it is then advisable to contact a lawyer with expertise in speeding cases to look at them.
14 motorists appealed against their speeding convictions in relation to a stretch of the A27 in Hampshire on the basis that the signage was incorrect and won their case. This has opened the door for other motorists to contest their convictions where they were prosecuted for speeding along that particular stretch of road.
There have been some cases where the speed limit sign saying 30mph has been obscured, but this has been held by the court as no defence as there is a presumption that a built up area - an area with street lights and no other speed limit signs- is a 30mph area.
It's certainly no defence to say that you couldn't see the sign due to fog! If it's that foggy you shouldn't be going that fast anyway!
