The train takes just under 2 hours. If you are going by car, the journey is around 70 miles and takes a bit longer.
3.7 km walking. 4.7 km by car. If you take the circle line it will take 15 minutes.
About 2 miles
London is in London ....
If you are walking then it is 0.7 miles, because you would go over Victoria Embankment. However, if you are travelling by car or taxi then it is 1.5 miles, for you must cross the Waterloo Bridge.