Met Police NIP Westway - Average Speed Cameras

[Man in the middle]

Indeed. The National Police Chiefs' Council's guidance for speeding enforcement suggests action should be take at (Limit+10%+2mph) so 35mph in a 30mph limit. 

 

Average speed cameras are probably the most accurate of the devices used. They simply measure the time taken to travel a known distance. Bear in mind that unless you were travelling at precisely 35.3mph for the entire stretch, you would have been travelling at more than that speed at some point.

 

You must complete and return the "request for driver's details" regardless of any issues you may have with the speeding allegation. Failure to do so will see you commit a separate offence which carries six points. You will almost certainly be offered a speed awareness course for that speed (they are offered up to (Limit + 10% + 9mph)) provided you have not done one in the last three years. It will cost you around £100, but no endorsement or points.  

[Man in the middle]

Just a point of pedantry on the above: the notice cannot be challenged. It is simply a notice warning you of possible prosecution. The only avenue of challenge you have opens up when you have declined (or ignored) any out of court disposals the police may offer you. In that event you will be prosecuted in court and you can plead not guilty to the charge. The Notice will play no part in that prosecution unless you suggest it was deficient in some way (for example, if it was served outside the 14 day time limit).