Speeding

Hello i was travelling along the x Rd north on the 29/9/09 at 11:00 am the weather was fine as i approached the speed camera site i checked my speedometer and it was reading approx 33 Mph as i got closer to the camera it flashed this flash was so intense it caused temporary blindness for a couple of seconds (see attachment) when my sight had returned i checked the speedometer again and it was reading approx 29 Mph. I thought no more of this as i assumed it had flashed somebody else.My assumption was wrong as i received a NIP dated 29/09/09 in October within 14 days of the alleged offence i think, i have pleaded not guilty as the speed recorded on the NIP is 41 Mph?.My questions are 1,What would make a camera give a recorded speed of 41 Mph when i know i was travelling at 33 Mph. 2,This type of camera is a Truvelo forward facing type would it be unlawful to use this type of camera without the approved level of magenta opacity required for the purpose of front capture. As the attached photo shows the flash was so great it makes daylight dark also the van on the opposite side of the roads rear reflector is visible, also i cannot make out my face in the car.

Any advice would be vary appreciated