Mark Nuttall - Slab vase is simon leach quite early I Think
James - Its not one of Simon's pots, despite the seal looking very similar and totally understandable as to why you might think that. It might be a potter called Len Stevens who is always being listed as Simon Leach on eBay.
Pat - Must be my eyes, because my book has a mark quite different to this for Len Stevens.
Peter Day - It's by Laurie Short, a Cumbrian potter. I've seen several of these pieces and once got into trouble with Simon Leach for listing one as his on eBay. He's not in any of the books. Simon Leach has himself suggested Len Stevens, but he only makes ocarinas.