For all types of mower belts I always use Marksman Industrial, Aldershot.
graham taylor, August 2011
I got a belt for my Westwood W11 from www.thebearingshop.co.uk.
You need to measure the circumference of the belt and check the profile. I think I got a standard v belt but I can not remember the circumference because it was about 3 years that I replaced the belt.