Pottery Charger or Platter - Makers Marks?

Does anyone recognise the impressed mark on this 30cm platter / charger? Unfortunately this is one of those marks that is apparently valid when read upside down (so the single letter could either be a 'W' or an 'M'. The conjoined letters above (or below!) look like possibly a backwards 'C' and a 'G' or it could easily just be something like a very stylised 'T'. I've searched the books and British & Irish Studio Pottery marks but without any joy.

Thanks for your help!

JGM maybe. Not a mark I've come across before

Thank-you, Naomi. It's certainly got me scratching my head!