Hello Mickyb, so sorry to hear that this is still being pursued.
The experts here have been able to assure you that the tickets and route that you took were valid on the day (although we don't know which day that was - you need to provide evidence of your delay).
Upthread, there was debate about whether a different operator needed honour your ticket, this is central to the matter. Apologies if someone has posted this already, but paragraph 9.4 of the current National Rail Conditions of Carriage states this:
9.4. Where you are using a Ticket valid on a specific train service or train services (such as an ‘advance’ Ticket) and you miss a service because a previous connecting train service was delayed, you will be able to travel on the next train service provided by the Train Company with whom you were booked without penalty.
'Booked' (my emboldening), is the key word. Any reference to Northern and XC being different operators is irrelevant. If things happened as they were described by you, the conductor on the Cross Country service to Birmingham was obliged by way of those Conditions to accept your ticket, even if you were using multiple tickets for your journey (
paragraph 14 applies).
Good luck tomorrow.
[Edited to add: Amongst the paperwork that you have received there should be a witness statement from the conductor / train manager on which the prosecutor has relied. Have you received this? What was the justification for their actions?]