If you have recieved a NIP in the post (notice of intended prosecution) then you are fooked, my Mrs got one for doing 38mph in a 30 zone and we wrote to them trying to blag it to no avail,
There used to be loop holes but as stated above I think the smokey bacon crew have now closed these off, there is a site
www.pepipoo.com or something like that, it has info on speeding cameras etc
At the end of the day if you know the camera's are there take your foot off the gas and/or buy a snooper,
Luciano