The biggest difference between a green car and the ordinary car is that the seating layout of the green car is 2x2 and the ordinary car is 2x3. Japanrail.com reports that the the green cars have larger seats, more legroom, more luggage space than Ordinary Cars and are all reserved seating while ordinary cars have reserved and non-reserved seating.

http://www.japanrail.com/JR_trainandseattypes.html


If you go to http://www.japanrail.com/links/eupore.html they list all of the distributors of the Japan Rail Pass in Europe. I tend to purchase them from JTB via their NYC office. JTB does have an office in London.