Yes, Eddie is quite correct and you need to be careful.
If you were stopped at the time of the offence there is no need for the authorities to ask whether you were driving as they already know. However, if you have been formally asked you must respond. Failure to do so is a separate offence which carries six points.
If you have been offered a fixed penalty (£100 and three points) and you do not accept it within the time allowed the matter will be escalated to court. You will have to plead not guilty and opt for a trial. Presumably you were stopped by the police who must have measured your speed. The officer will be called to court and his evidence will be that he stopped you, he confirmed your identity and he will also testify that you were driving a vehicle that exceeded the speed limit. The fact that he mis-recorded your Reg No is largely irrelevant. That’s all he’s done and his evidence will be sufficient to convict you.
If you are convicted you will receive an income related fine and either 3 to 6 points or a ban (tell me the alleged speed and the limit and I’ll give you more details of what to expect). You will also pay a surcharge of 10% of the fine and prosecution costs of around £350 (but this could be more depending on how much work is needed to prepare the case for trial).
My advice – don’t try to fanny about with this. Accept the fixed penalty because £100 and 3 points is the best result you’ll get.