For those who don't know, Eurostar have two main routes they run from London to mainland Europe. One goes to Paris, the other to Brussels. Both go through Calais and Lille. However, generally only the Brussels services stop in Lille, at Lille Europe station. On the whole, the Paris services are more popular, so the cheapest fares on those sell out first. Moderately last minute, there can be only expensive tickets left for Paris. At this point, on the whole, cheaper Lille tickets still remain! So, what you need to do is first buy a ticket from London to Lille Europe on the Eurostar. Single or return, as you need, but be aware that two singles is more than a return. Next, using your favourite non-evil rail booking website (eg loco2.com or captaintrain.com), book a ticket from Lille to Paris. These can be had for about €20 in advance, slightly more last minute. If the train is a Lille Europe to Paris train, great! If it's a Lille Flandres to Paris, then you've a 5 minute walk. The walk is fairly well signposted from both ends, head to the middle of Lille Europe station, down the escalator, past the giant plant sculpture and the Euralille shopping centre, and into Lille Flandres. There's a metro too, but it'll probably take longer... Coming back, be aware of the 30 minute checkin deadline for Eurostar when deciding what train to get from Paris to Lille! If you have time, there's a big park outside the station, a large shopping centre with a supermarket where you can stock up on French wines / beers / cheeses, and you're a 15 minutes walk from the great restaurants and bars of old Lille (Vieux Lille) Booked 120 days out, a London to Paris ticket is cheaper than changing. Closer in, a London-Lille Eurostar and Lille-Paris TGV can save you money, so price both up before booking an expensive London-Paris ticket!