Like Jackiecj, I was charged with the job of looking after the Green Shield stamps, I seem to recall that Tesco gave them out as well, my Mum used to go to the one in Rhos On Sea a lot (now the Spar). We used to go over to Rhyl where there was a large Green Shield Stamps catalogue shop for getting the goodies.
One thing I didn't know was that when Green Shield Stamps shut down, all their catalogue shops kept going under a new name...Argos!