Unfortunately, exceeding speed limits is an offence. And exceeding the highest speed limit, is a serious one.
In this case, you have received a notice for a Single Justice Procedure.
This kind of notice is sent by the Police when they want to commence Court proceedings for a driving offences, proceeding for which a hearing could not be held if the Magistrate thinks there is no need for it to be held.
You have the option to plead guilty or not guilty, and, if you plead guilty, you have the option to present a mitigation in writing to claim mitigating circumstances to try to minimise the penalty.
However, this is not something for do-it-yourself, and you should consult a motoring solicitor, for a thorough assessment of your circumstances.
This is advisable even more considering that the recorded speed was only 10mph above the speed limit and I understand this is your first offence.