Thanks for the information and the time.
I am sorry but I cannot give you good news then. I’m afraid you are in difficulty here.
These fixed penalties are an invention of the police. They don’t exist in law. They certainly weren’t provided for by Parliament. The purpose of them is to divert cases from court.
The reality is that, come what may, your licence was not a UK one so they couldn’t add points. I realise that you say that isn’t your fault but that doesn’t change the fact. They have turned to a summons because they only have six months to lay an information or they will be time barred.
The question is whether you have a defence to the substantive charge. If you were going to accept the FPN then I suppose not.
If you plead guilty though and mitigate on the basis that you tried to accept but failed for whatever reason then they may give you a fine of £85 and the surcharge of £15 plus 3 points. I have seen magistrates do that many times. It can’t be guaranteed though.
I'm sorry this isn't the answer you wanted but it is the position that you face and I have a duty to inform you truthfully.
Hope this helps. Please let me know if you need more information.