Did you know that every time your car goes past a speed camera, even 1mph over the set limit, it is registered and put on a database? You only get a ticket if you are way over the limit or, (this is the bit that I didn't know) if you receive over 10 near misses, you will be classed as a serial offender and get a ticket the next time you go just over the limit.
This is why you hear of people being done for 34mph in a 30mph limit area, whilst others doing 39 do not. You can check what has been registered against your vehicle at the following web address:
Just enter your car registration. If there is any data on your vehicle you can click on the camera window to see a copy of the photograph .
Hope it's useful.
If the link doesn't work just put "i-database.co.uk" in Google.