Thanks again for the advice so far, I went back and told them that I had already contested the penalty in previous correspondence.
However they've come back and said.
We received your appeal, however the owner of the vehicle is held liable for all Penalty Notices issued on Railway assets in all circumstances, as such we have no cause of action against the driver or hirer of the vehicle.
And they want paying in the next couple of weeks.
I'd be grateful for advice on the next response...