Leigh - Just a guess from looking at my book - Marilyn Williams, Plumstead London??
Chris Parker - This is a comemoration mug by Mary Wondrausch Brickfields Pottery. A nice piece and much sought after, though the seal is not quite complete.
James - A nice litte Mary Wondrausch beaker. You see them appear on eBay from time to time - they normally go for £20-£30ish (at the moment - should be going for me I think).
Denise - Just to say, thank you all for your information. It is much appreciated!