I know for a fact that they do use LTI20-20 but they may use other devices as well including mobile gatso's.
Have you recieved and returned a NIP?
Do you know what speed they are alleging?
If you saw the van and they were videoing the front of the car then it was almost certainly the dodgyscope. So far only a couple of exceptional cases have managed to get a copy of the video.
You might want to take a look at some threads and ask for advice at
the Pepipoo forums if you havn't already.
They will try to bully you into taking the FPN, they will then try to bully you into pleading guilty. Most of what they say is completely false. You can change you plea right up to the actual hearing and magistrates are often very understanding if you explain the situation you were put in. (i.e. having to plead not guilty to satisfy yourself of your guilt or otherwise).