The Ordinance Survey blog has a post on the route.
I have cycled two sections; most recently a section from Bradford on Avon [which the OS blog accurately describes as 'a gem of honey coloured stone houses'].
|Canal at Bradford on Avon|
I hired a bike from Towpath Trail, an efficient bike shop which has a large stock of mountain bikes for hire, and had a very pleasant few hours going west towards Bath.
There are several trails and canals running off the route.
|Entrance to a side canal|
There were a lot of boats on the canal. Some were hire boats, but there were also many rather decrepit boats belonging to people who appear to live full time on the canal. I suppose living on a canal boat is a good way off staying away from the gaze of Britain's surveillance society.