What is the Cheapest way from southamton to London?

By National Rail - from around £43 return: Direct rail services travel to London Waterloo every 45-60 minutes; the travel time is about 65 minutes with faster journeys about 50 minutes.

By coach - from about £18 one-way: Megabus, National Express and Oxford Tube, run direct coach services; travel duration takes a couple of hours 15 minutes to almost 3 hours. It may not be comfortable especially at the peak and during the holiday season