If you genuinely believe that you were not speeding, you are entitled to ask the police to see their evidence that you were speeding. In the case of speed cameras you are entitled to see the pictures. There have been cases where the number plate of speeding vehicles has been misread.
A speeding conviction has sometimes been avoided where the owner of the vehicle does not know who was driving. In such a case the owner must make every effort to discover who the driver was.
It is no defence to say that there were no signs warning of speed cameras. However it may be a defence if there were no speed limit signs or if they were obscured.
If the owner does not receive the Notice of intended prosecution within 14 days or if there are significant material mistakes on the NIP then this may be a defence.
If you think you may have a valid defence to a speeding ticket then you should consult a motoring lawyer for expert advice and guidance.