sallyanna
you best source of info on the internet about this is Pepipoo. Try posting your question there.
http://www.pepipoo.com/NewForums2/viewforum.php?f=5
Not sure what you are describing, usually the notice of intended prosecution (NIP) and S172 request for information are combined in a single document. Sounds like they've sent back the NIP/S172 because you have given them 2 names. This is called 'unsure of driver defence' and it is not trivial because you must be able to prove to the magistrates due diligence in trying to establish the identity of the driver at the time of the alleged offense. It is likely that if you continue with this line then the registered keeper (you?) will be charged with 'failure to supply' under S172.
arthurdent