This is the best fabric shop I have ever been too, it is completely mad and unique, they always have great advice (especially if you go on a Monday, Wednesday or Friday - the woman who works on these days is lovely)
Once you have been here you won't want to go anywhere else, they have fabrics with pea pods, tractors, cups of tea, cherry pies... seriously they just have everything! Also great for buttons, beads, ribbons and random bits and bobs that you didn't even know you needed.
It's situated in Petworth market square (GU28 OAH) called Prince Fabrics - I'm sure they'd send you some samples of whatever you are looking for in the post if you can't get the time to travel there but obviously I'd recommend actually going there just to see it because it looks like Aladdin's cave. Word of warning though, it is quite pricey and you will want everything!
This is Louise in her shop, holding my A2 project.
Also there's loads of really interesting antique shops in Petworth and of course Petworth House, which is amazing and has loads of Turners art.