A width of 1.2m is the minimum for wheelchair use, with 1.7m allowing two wheelchairs to pass.
I just wanted to bump this topic to the top to demonstrate how well viewed it is, despite there not being any activity for nearly three years.
Someone is searching for this information;-0)
See also Sensory Trust for concise gradient and camber regulations etc.
Regardless of the regulations, its is good to have an awareness of the potential access for all in a garden. Great to see this being discussed here! :)