Lynn are you sure what type of speed gun it was, i.e. Radar or Laser.
The top right photo in the Sunderland Echo appears to show a laser speed camera van, possibly an LTI 20.20. If so then they are allowed to be used from inside the van through an open port without glass, but then there should then be a video, which you should be able to get through the Data Protection Act or, if you have taken the case to court, through the discloser rules. That might contain sufficient information to check the validity of the speeding allegation. With a radar system there might also be a video, or at least photographs, which might similarly be of help.
You can find out with a Freedom of Information request to the police asking what equipment was used at that location and time, but I would have thought it would tell you on your summons. You should certainly be able to get such information through the disclosure rules if you have gone to court.
At a hearing you could ask the Magistrate, or write to the Crown Prosecution Service, stating that you make a formal request for the full disclosure of the evidence under Section 7 and 8 of Chapter 25 of the Criminal Procedure and Investigations Act 1996, which requires that: “The prosecutor must disclose to the accused any prosecution material which has not previously been disclosed to the accused and which might be reasonably expected to assist the accused's defence . .”. Then state what it is that you want to be disclosed.
If you get a photo, or photos, from the speed camera, it might be possible to determine the location of the camera, particularly if it a laser and also gives a distance reading, but that would not verify the location of the speed gun which, if radar, might be a separate component outside of the camera van. Any photos, from the speed camera you could show could help to identify the type of equipment used.
Have you also tried the PePiPoo site,
http://www.pepipoo.com/ , to find out more about the legalities of the situation.
Are you able to get any legal advice or representation, particularly for your day at the trial. Without some help from a legal advisor , the police and prosecution may out manoeuvre you in various ways, since they know all the tricks to use, and it is an everyday issue for them.
I wish you every success in this matter, since having been through the process myself, and seen what others have experienced, I understand how daunting it must seem for you.