Dear all,
As promised, I'm posting to let everyone know the outcome.
Sent letter to Northern on 17/08/15 and phoned into today (3/09/15) to check on progress. Coincidently Northern made their decision not to prosecute this morning and so I paid £80 + fare owing to ital-uk over the phone.
I'm relieved and am very aware of how lucky I am to have this offence pardoned and kept out of court.
Behaviour never to be repeated again.
Thanks to all for the guidance.