Right, first things first, lets get things into perspective.
A bike has been recorded exceeding the speed limit and the registration number has been recorded, therefore a Notice of Intended Prosecution (NIP) is required to be sent out to the registered keeper so that it has a reasonable chance of arriving within 14 days of the date of the alleged offence.
The arrival of an NIP does not guarantee that you are being prosecuted, it is just a requirement to notify the registered keeper that Consideration to the question of prosecuting for the offences of…is being given.
Forgetting any evidence at the moment, you need to notify the Police of the details of the registered keeper and/or the rider at the time. Failure to do so is a seperate offence regardless of any speeding matter.
You can include a covering note stating that you have included details of the registered keeper (I assume that this is you) but you can also say that on the date in question and at the time you were (enter location) and that you were driving a car that you had hired from (enter details) which confirms your presence elsewhere and that you are prepared to produce this evidence at court.
Also confirm that your bike was locked up in a secure garage or wherever it is kept and that nobody had your authorisation or permission to use the bike. You could then suggest that you suspect that either your registration number has been written down incorrectly or cloned.
This may have the desired affect of binning the whole process there and then. But if they decide to go further, then you will receive further correspondence detailing what the next process is. If they decide that they are going to continue with a prosecution or offer a fixed penalty, then that is the time you start asking for evidence and you consider sorting out a defence. If it gets to that stage, then let me know and I can put you in touch with someone who can assist you and represent you if needs be.
At this stage though, don’t start panicking about prosecutions or anything like that. If you are really cncerned though, then nip into your local Police station with the paperwork and they can always speak to the central ticket office (or at least they should) on yur behalf and they will be able to advise you of the best way forward.