Janet - Hi, This looks very much in the style of Joanna Wason, who worked alongside Janet Leach at the Leach pottery before it's closure for refurbishment, she now pots from home.
Fliss - I think the previous correspondent may be right. Check out www.studio-pots.com/JoannaWason. See what you think.
Trevor - Hi thanks for your comments. I contacted Jason Wason who advised me it wasn't made by Joanna Wason
nick - just a thought...judging from the (apparently) heavy glaze - have you thought Trevor Corser? sometimes it is possible to discern a mark if you hold to the light at just the right angle