what bus lines go to paris from london?

Answer 1

There is a direct bus from Paris to London, (it will use one of the ferries or the train for cars through the tunnel,) even when you have to get out of the bus at the ferry your luggage stays in the bus.
This is the English site for the best known bus line, there may be more lines.
http://www.nationalexpress.com/eurolines/home/hp.cfm

Answer 2

Going by TGV Train is your best option. The trip is only 2 hrs 45 mins from Waterloo to Gare du Nord. Book early for low prices.

If you are determined to go by bus, you'll have to go from London to a port city, take a ferry across the Channel and then catch bus to Paris.

Answer 3

You have to cross the water. There is an underwater (tunnel) train that goes to Lyon, France - you can probably take a bus from there to Paris or just use the eurorail trains