I may have mis understood the conversation he had with the woman standing in the vestibule where he wanted to know why she didnt buy a ticket before boarding and told her it was 20 extra for a penalty fare. Maybe he was just bollocking her and didnt actually charge her - but she was none too happy.
he might have been having a conversation about the 'buy before you board policy' in relation to purchasing tickets on board the train at 'manned' stations. if the figure of ^20 was mentioned that would relate to the ^20 or twice the single fare to the next stop which ever is the greater amount type conversation that a penalty fare inspector would have or a tm would have if advising a customer that "should a penalty fare inspector have been on this train then they could........" which is a conversation tm's do have with customers if travelling in a penalty fare area, even if they themselves cannot penalty fare. bearing in mind twice the single fare to newbury is greater than ^20 it would be more than that anyway