Country / Art Pottery ewer inscribed XY, probably Farnham Pottery

I know that it's a bit battered but it's just such a good old piece of country or art pottery. 9" tall, uneven powdery blue glaze (black in places) with streaky yellow interior (plus a pool of really thick glaze inside), over terracotta clay. Inscribed 'XY'. Any thoughts anyone?

The only item I have seen marked like this was a bit of Farnham pottery. The two letters on the bottom stood for the colours. Not certain what colour starts with X but Y could be yellow the colour inside the jug. If its Farnham then its around the first world war and sold in very nice stores as a bit of country art pottery. You can find some information on line about Farnham that could clear up the X thing.

Thanks for that, both. A cursory look at other examples made Farnham a good candidate.