The conductor later filed a travel incident report and Northern sent a letter to Mr Williamson, asking for an explanation of the circumstances in writing within two weeks.
Mr Williamson said Northern had sent another letter notifying him of a potential prosecution.
Earlier he posted on X, external he had been contacted again by Northern, who were “confirming that they will ‘be taking no further steps against [me]'”.
Mr Williamson said he hoped customers in the future would not be “caught out by obscure railcard terms and conditions” and that the government would “step in to stop train operators bringing cases like mine through the courts”.
The Department for Transport said earlier in the week: “Ticketing has become far too complicated, which is why we have committed to simplifying it for customers, as part of the biggest overhaul of our railways in a generation.”
They added they expected Northern “to ensure their policy on ticketing is clear and fair”.
