In trying to get the police prosecutor’s agreement should I mention that the NIP was not served correctly and that there is some evidence of a poor postal service to my address. Or again is it best to keep it simple and don’t give them more than what they need to know.
Just keep it simple. Make your offer. Only volunteer more information if you are asked and all you need to say then is that you did not received the NIP and request for driver's details.
What happens if they don’t do the deal? How do I prepare for that? A statement of facts and print off the Royal Mail claims email chain.
As far as I am aware here has only been one instance on here where the deal was not accepted. In that case the defendant was less than polite to the prosecutor, telling him what he could and couldn't do. So the prosecutor showed him.
In the unlikely event you do need to defend the "Fail to Provide details" charge it is unlikely that your trial will take place on that day. Instead it will probably be adjourned to a later date. However, if it does proceed on the same day all you can do is to take whatever evidence you have of earlier problems. I have to say that to cite one particular item going adrift does not seem to make a very convincing argument. I would imagine most people could do that. However, if that's all you have, that's all you have.
If I am found guilty of both offences, then I believe, the points on my license would take me over the 12-point limit. Can I appeal after or is it best to set up mitigating circumstances on the day.
Unless you plead guilty to them both you cannot be convicted of both offences. You cannot be convicted of speeding because the police have no evidence that you were driving. If your offer is rejected and the police proceed with the Fail to Provide charge, the speeding charge will be dropped. In that event the worst that can happen is for you to be convicted of the Fail to Provide charge and that can only result in six points. Would that take you to twelve or more?