We did some research into an overland trip between London and Barcelona, looking at journey time, cost, carbon footprint and the hassle factor for journeys by train, plane and car. The graphs below reveal the results.

By train an overland trip to Barcelona is more difficult to book than a flight, with visits to several websites needed to buy Eurostar and TrainHotel tickets. You leave work just after lunch on Friday to get the 15:30 Eurostar from St Pancras, which gets into Paris at 18:54 - you can finish off some work if you like on the way. You get the metro across Paris to the Gare d’Austerlitz, where the TrainHotel sleeper leaves at 20:34. You can spend the evening in the dining car before going to bed. On Saturday morning you arrive at the station in Barcelona at 08:24, ready for breakfast and a full day ahead of you. Your carbon footprint is a tiny fraction of other methods.

By plane you can't get there first thing in the morning - you can either take the Friday off and get there at lunchtime after a very early start, or leave on Friday afternoon, getting in late to your hotel after an airline meal. Booking of course is much easier, but your carbon footprint is a disaster, up to 20 times as much as the train.

By car you can of course leave when you like, ferry/shuttle permitting, but unless you are really going for it you'll have to stop for the night somewhere in France, making this a slow and costly way of getting there. Your carbon footprint will depend on your car, but for two people will still be more than double that of the train.