Sounds like 'cosine error' where the device was not straight on to the car being measured or worse operator 'error'.

Cosine error would be in the drivers favour.

Update:

To cut a long story short I sent them a letter stating that I didn't believe I had been speeding and could they provide me the photographic evidence and to check the equipment etc etc. Heard nothing for weeks then got a letter this morning stating that they were not pursuing the speeding offence.

Goes to show if you think you are innocent its worth pursuing.

Well done LHS.

What about all the other motorists like you who were clocked wrongly that day by that van? Wonder if they'll be stopping proceedings against them also? I somehow doubt it.

Well done mate. Good course of action, and it's worked out well. 🙂

Thats the trouble, guilty until proven innocent. Well done for sticking to your guns!