The Grand Western Canal is a very nice restored canal starting (or finishing) in Tiverton, Devon. Sheltered and flat water make it a perfect place for first paddles. The canal still has a horse drawn barge which you can get a ride in and the visitor centre gives full history of the canal from building to regeneration.
Just a short paddle gets you out into very unspoilt countryside. With camp-sites along the way and easy access for paddlers it is surprisingly quiet on the water. Highly recommended for relaxed paddles.