im in kent and have a few years had ribs.
id be more than happy to assist. as per the previous post the process is very much like fixing a puncture in a bike tyre, although you need speciifc cleaning and preperation materials, special two part glue and of course the right material for patching.
Most/many/some chandlers stock repair materials and the correct adhesives.
it is important to use the correct adhesive ( not bicycle puncture repair glue!).. there is one adhesive for PVC and another for Hypalon. Use the 2 pack versions for major repairs
You could try Clydach Marine in Sevenoaks http://www.allgoodfun.com/ He'll probably have the repair kits and he might know of somewhere in the area that does repairs.
Other wise all the repair materials are available from Polymarine