If asking for photos, do not ask for/use the word 'evidence', use the phrase 'to assist in identifying the driver'. You will not get 'evidence' until you are going through the court process. If you get photos post a question on pepipoo.com or other forums to get an opinion as to whether or not there may be a problem with the 'ping'.
The most important thing to remember is that the 28 days you have to return the S172 request to name the driver does not stop just because you requested photos.
You could get photos od the location of the signs, check the documentation that the speed limit signs are in the right place, check that the traffice order for the speed limit is correct ( from the town hall) or you could just pay the fine and take the points.
A final thought, find out if the local scameraship offer a speed awareness course. You would qualify for 36 in a 30 but it may depend on whether or not you have existing points. It costs ca �80 but no points.