Most of England is a 2 hour train ride from London.
Seriously, you can't get more than 70 odd miles from the sea anywhere in the country.
I lived in London for a few months years ago, within walking distance of Greenwich (pronounced Grennich so you don't sound TOO much like a foreigner
). It's a wonderful city, unlike anything, anywhere here. From what I hear the Thames has been hugely cleaned up since but when I was on it, it was possibly the single most disgusting place I had ever been - an ancient open sewer. I'd go to the coast if I wanted to go sailing.
My best advice for travelling there? Take lots of money - LOTS of money. It's a wonderful city to be rich in but if you've got the shorts, not nearly so much. I think you will be stunned by the cost of everything there.