The main hurdle is train times. Services on the London/Lille route are limited, so my choices are a 5.27pm train, arriving in Lille at 7.54pm (France is an hour ahead), or a 7.34pm arriving at 9.54pm. Though I work only 15 minutes from the Eurostar terminal, the earlier one relies on flexible working, as you need 30 minutes at St Pancras to check in. And crucially, to get the most affordable deal — a £55 return — you need to book up to two months ahead and can't switch trains, which limits post-work spontaneity. On-the-day tickets are expensive and not always available.