If and when you have accepted you are the driver ask for a copy of all the evidence under the Data Protection Act, particularly if it is an LTI 20.20 video, as it is then personal data held by the police about your movements.
For this you write to say something like, “I am now making a Subject Access Request under section 7(1) of the 1998 Data Protection Act that you provide me with a copy of all the data you are holding with respect to the speeding allegation you have made against me”.
It is important that you do this as soon as possible after getting the NIP if you want to see the evidence before the expiry of the Fixed Penalty Offer.
The police may try to claim exemption from the Data Protection Act because it is evidence for criminal proceedings, but that claim by them was not upheld by the Information Commissioner's Office, so let me know if that happens.
As pointed out by Anton, it would also seem that under the Data Protection Act 1998, Chapter 29, Part IV, Exemptions,
http://www.opsi.gov.uk/acts/acts1998/19980029.htm
Disclosures required by law or made in connection with legal proceedings etc.: Section 35.
(1) Personal data are exempt from the non-disclosure provisions (i.e. not exempt from disclosure) where the disclosure is required by or under any enactment, by any rule of law or by the order of a court.
(2) Personal data are exempt from the non-disclosure provisions (i.e. not exempt from disclosure) where the disclosure is necessary, (a) for the purpose of, or in connection with, any legal proceedings (including prospective legal proceedings), or
(b) for the purpose of obtaining legal advice,
or is otherwise necessary for the purposes of establishing, exercising or defending legal rights.