I got all the information that I wanted from here:
http://www.rootschat.com/links/0x8c/ A link to Treorchy library.......... I think that they referred me to Rhondda Cynon Taff bereavement services who have the information.
I was able to get the plot number and the burial certificate. You do need to have a death date for them to search for info. We went to the cemetery and although I was promised that the plot number would be marked for us, it wasn't, but a very helpful man was there and was able to guide us to the right grave.
Treorchy cemetery is very big and on the side of the mountain really, if you visit in the winter make sure you have warm clothes on, it's freezing.
Anne