mike - Hello, it is a stylised A and O, from a male potter whos name completely escapes me. Will have a think.
Richard - I think this was made by Andrew Osbourne (the partner of Jennie Hale) at Longham Pottery near Okehampton in Devon
Sally - Thanks for your help. Someone else also agreed that it was made by Andrew Osbourne.
Ann - I have two pieces by Andrew Osbourne and they are the same style,pattern and colour as yours