If all you have so far is a Notice of Intended Prosecution (NIP) then you won't have any supporting documents.
In fact with many forces you will have to plead not guilty before they will let you see <b>any</b> evidence. You only have their word that a crime even took place.
If it is the NIP you have then you have 28 days (which can often be extended) to reply. Use those 28 days wisely. Do your research.
Some forces will send a fixed penalty notice with the NIP, they shouldn't really do this since without the NIP they have no evidence of who was driving. If you have been sent both then I would definately ask on the Pepipoo forums for advice.
What should happen is.
day 1 you trigger speed camera.
by day 14 they post NIP to registered keeper.
Registered keeper has 28 days to reply nominating driver.
If keeper nominates themselves then an offer of fixed penalty will be sent, unless the case is to go to court (Speed well over the limit or driver close to ban under totting up), in which case they have six months (from the date of the offence) to lay papers with the court.
If keeper nominates another driver then that person should be sent a NIP to which they have 28 days to reply.
If this person nominates themselves then an offer of fixed penalty will be sent, etc.
After recieving the offer of fixed penalty you then decide if you are going to go to court or just pay up.
If you want to see any evidence you may have to refuse the fixed penalty.
The NIP(s) do not have to be sent through registered post and the police/CPS/scammers only have to prove they sent it. If your postman loses it and you don't reply within the 28 days you will likely be charged with both the speeding and failure to notify (S172). Of course without a completed NIP they have no evidence as to who was driving but they will try to weedle that out of you in court.
If you chose not to fight it's your decision, and I can understand that. But make it a decision based on the facts, not the half truths (and often bare faced lies) you will have been sent by the scammers.
There have been a number of cases where proecutions have been pursued where it has been found that the cameras were enforcing a limit which did not exist (see
Folly Bottom). It was only because someone fought the cases that, in some cases THOUSANDS of fines have had to be repaid. Unfortunately no compensation as yet for anyone who may have lost their job due to being banned for an offence which never happened.
And
another case in N. Wales.
And
another.
So much for "you have nothing to worry about if you stick to the speed limit".