Thank you guys for all your messages, advice and wisdom.
Just to clear a few things up...
I did not accuse the guard of being racist. I asked him if he 'was' racist... as I said, I felt victimised and couldn't think of any other reason as to why he was picking on me. It may surprise you to know the guard was of asian origin. Anyone can be racist no matter what race they are from. But like I said I did not accuse him, I asked him, and as I said before, I regret it. It was not abusive language. I did raise my voice when demanding my ticket back but I never once swore or used offensive language. I have been accused of :
'Using threatening, absusive, obscene or offensive language'
'entering a train for the purpose of travelling without a ticket entitling travel'
The pen I used was actually one I have used on numerous occasions, and been checked by guards with no problems. I have however had problems in the past when using a biro which tends to scratch the shiny surface of the ticket and can look as though it has been tampered with. I thought the rollerball was better solution but alas not on this occasion.
Well, I have decided to write the letter, keeping it as factual as possible and not using emotive language. I still think the inspector and the cop were bang out of order and I will get a solicitor if necessary.
I will let you know how it all goes. I have worked for the NHS now for 14 years with exemplary references. Fingers crossed this matter will not mar anything I have worked hard to achieve.
Thanks again