What you probably have isn't a NIP, but a s172 notice asking you, as the registered keeper, to name the driver at the time of the alleged offence. You must do this within 28 days or face a fine of up to £1000 and 6 points. What was the location and where you say you think you were at the time., can you post that on here, it may help us to help you.
Edited to add to take note of what SlithyTove says above, both posted at the same time!
Obviously I have to comply wth the S172, but doing that triggers the course offer, but it also sort of admits to being at that location at that time, how do you get round this double edged sword ?