what is the proper name for 'welsh bells' please

Sorry I'm Welsh but I do not know of a Welsh Bells only the Welsh Poppy, but I would immagine it could be one of the Companulas(Carpatica) species of bell flower there are a few types and different shades of Blue try Googling Companulas low growing and see if you can find it.

It's probably Campanula carpatica, as Telme8 says, or campanula muralis, if it's low growing and in flower now.