Unfortunately if you decide to go down 'the prove it was me' route they will probably just tell you what they told me a few years ago, that you will have to go to court and let the judge make the decision (and we all know how that will end up) resulting in far higher cost than a simple fine. My car was photographed doing 42 mph in a 30 limit, from the back view, so the driver could not be seen at all. My problem was that my wife and I shared the drive of this route twice a day taking our son to school, we just did not know which one of us was driving at the time. Explaining this to the police by letter, all I got in reply was "well if one of you doesn't own up to it you will have to go to court. I checked with my cousin, who is a barrister, and he told me that the right in law not to incriminate oneself does not apply in this case (it's ok if you are a murderer because it does apply!). I had to bite the bullet and say it was me driving and, to this day, do not know if it was!
If you finally receive notice of prosecution, my advice at this point would be to ask for photographic evidence and put the question to the police how they could be sure it was you speeding when you were in a long line of bikes. If you get the response that I did I think you will just have to accept it and move on. Good luck, I hope it works out better for you than it did for me.