Simple question really, - I am attending an appointment at Guy's Hospital today and will be travelling from St Albans direct to LBG on Thameslink. I intend to get a super off-peak London Thameslink return ticket, but NHS appointments being as they are, it may mean that I am not able to catch the last afternoon train home before the evening peak. I will then need to excess the ticket to travel and in view of my current need to limit my walking, would prefer to do that in a proper ticket office. It isn't clear if there is one at LBG and where it is. Could anybody please advise of the situation there?