I think I've discovered the origins of the piece following a visit to Mullion today

Our first port of call was Trecarne Pottery, where I met Michel Roux, who is absolutely lovely, and that French accent (swoon

). He spent some time talking to me about his work, and I've got my eye on a gorgeous celadon bowl which is now on my birthday list.
Next port of call was the village itself. No other pottery studios, but a couple of galleries selling various art stuff. The owner of one remembered a pottery workshop many, many years ago in the late 60s which was now a private house, but couldn't remember the name of the owner.
Things were looking a bit bleak, so we decided to pop into the fish 'n' chip shop before heading back home. Whilst waiting for the fish to fry I just happened to ask one of the three ladies who worked there if they knew who could have made the piece. Can't believe my luck! They knew the name of the owner of the studio/workshop of the now private house, and confirmed that they use to inscribe pieces with 'Mullion'.
Frank and Jane Day worked from there in the 1960s. Frank had a kiln in the back garden. According to the chippie ladies, Jane was a little bit of a character. She had long bright purple hair which was plaited and wrapped around her head, with kiss-curls on her forehead, and 'shockingly' wore a chain around her ankle, which in those days was considered risque. The shop was called 'The Blue Monkey'. Both Frank and Jane are long deceased.