There are two issues here.
If there are ticket issuing facilities at the station where you start your journey that accept your chosen method of payment you must purchase a ticket before boarding the train. Appropriate ticketing facilities were available at your starting station because the ticket office was open but you chose not to use it because you arrived late. You committed an offence by not buying a ticket and boarding the train.
The TVM doesn't accept cash and the promise to pay feature is really something that should only be enabled when the ticket office is closed (similar to PERTIS machines back in the day). This might provide some mitigation if things were to turn ugly.
The behaviour of the revenue staff is unacceptable and this should be subject of a separate complaint to Northern.
If there are ticket issuing facilities at the station where you start your journey that accept your chosen method of payment you must purchase a ticket before boarding the train. Appropriate ticketing facilities were available at your starting station because the ticket office was open but you chose not to use it because you arrived late. You committed an offence by not buying a ticket and boarding the train.
The TVM doesn't accept cash and the promise to pay feature is really something that should only be enabled when the ticket office is closed (similar to PERTIS machines back in the day). This might provide some mitigation if things were to turn ugly.
The behaviour of the revenue staff is unacceptable and this should be subject of a separate complaint to Northern.