The Holmesdale tunnel, which is the tunnel by junction 25 on the M25 is going to have SPECS cameras fitted in it. They are rear facing ones so bikes will be read as well. These are very small CCTV type cameras which work on ANPR-type number plate readings. They are a set distance apart and read your number plate as you pass each camera. If you travel between the two in too short a time frame, then you are obviously speeding and your picture is taken.