davina - hi kate your item was made by keith smith, otterton mill pottery,devon.
unknown - It could be Keith Snith
Linda B - I have one of Keith's stoneware jugs in green with spots of red copper. The KS is impressed and doesn't look much like your signature image. I have a book 'British Studio Potters Marks' by Yates, Owen and Fournier which has his impressed signature which is identical to the one I have myself. You may be able to borrow a library copy to help you.