It appears that the rail replacement bus goes from Southampton Central to Southampton Airport Parkway where the train is boarded to London Waterloo with a change in Eastleigh. Since Eastleigh is about 6 or so miles from Southampton, am I wrong in thinking that I could get a ticket going directly to London from Eastleigh and take a taxi to Eastleigh from the Southampton Cruise terminal. It may be a bit more expensive, but I would avoid the hassle of the buses and the changing of trains.