Does the notice mention, perchance, "GMT" after the time stated? If so, and the time stated is one hour earlier than when the incident occurred (which you seem to recall) that would explain the "error" and so end any arguments.
If not, you must think this through.
Though it may not seem like it, you have been sent two distinct documents.
The first is the Notice of Intended Prosecution (“NIP). This must satisfy the requirements of s1 of the Road Traffic Offenders’ Act which says that a NIP must provide “…the nature of the alleged offence and the time and place where it is alleged to have been committed,..”
As above, you could try arguing that the NIP does not satisfy that requirement and so you cannot be convicted. The important thing here is what is mentioned in “Read me first”:
"Minor errors in a NIP, which do not negate the purpose of enabling the driver to recall the incident which gave rise to the allegation, do not void the NIP."
You seem to have a good recollection of the event. If you attempt to defend the charge on the basis of a deficient NIP you will almost certainly be asked, in court, whether or not you have that recollection. Unless you want to commit perjury (potentially turning a fine and points into jail time) you will have to say that you do. Having done that, the court will almost certainly find that the NIP fulfilled its purpose.
The second document you have is a “request for driver’s details”, issued under s172 of the Road Traffic Act. You could begin your response to that as BertB suggests, simply stating that your car was not at the location at the time stated, and see how they react. Waiting 14 days will make the issue of a second compliant NIP impossible. However, because of my view (above) of the validity of the one you have, I don’t believe it will make much difference.
The risk you take here is if you fanny about too much with making a valid response to the request, the police may simply proceed to prosecute you under s172. I would not rate your chances of successfully defending such a charge (especially bearing in mind the view I believe the court would take on the NIP). The good news is that in the event of an insufficient response to that request, the speeding charge is a dead duck. The bad news is that a conviction for a s172 offence carries a hefty fine, six points and an endorsement code (MS90) which will see your insurance premiums considerably increased for up to five years.
My advice would be to make an approach to the police to see if they are willing to discontinue the matter because of this discrepancy. If they are not, I would accept any offer of an out-of-court disposal they might make.
What was the alleged offence?
