Could anyone recommend what I need to buy in order to connect a Leica Summicron-M 1:2/50 E39 lens to a Canon EOS 5D body? Do I need a bayonet lens adaptor and if so please let me know which one?
There are no such adapters, because the Leica M lenses have a registration distance that would put the lens inside the Canon's body if you wanted to achieve focus to infinity. Canon's mount distance from the sensor is roughly twice that of a Leica M's mount from the sensor/film plane. The distance the lens is held is part of the mount system design and is critical for the lens to focus properly.
To shove the M lens into the Canon body and hold it at the appropriate distance, you'd probably also collide with the SLR's mirrorbox--something M-mount rangefinders don't have.
The only digital camera bodies that you can easily adapt Leica-M mount lenses for are the mirrorless cameras: Sony NEX (E-mount), Fuji X, and Olympus/Panasonic micro four-thirds cameras, where the registration distance is smaller than that of Leica M, and where you can use simple ring adapters. Be aware, however, that even though you can get the registration distance to work, there is still the issue of sensor stack thickness, particularly with wider fast lenses.