Here's some of my recommendations for suppliers that I've found both in and arround the southend area and also online stores.
The Strand Gallery - Southchurch road has a good range of art materials and framing supplies. A helpful shop that a discount for students.
Art Shop - Berrys Arcade Rayleigh - a small convenient store in Rayleigh
Laurance Mathews - Stocks a wide range of art materials.
Here's a few of the online store I use on a fairly regular basis:
Jacksons - Stock a wide range of art materials availible at discount prices including their own line of paints - free postage if you spend over a certain amount. approx £39
Great Art - http://www.greatart.co.uk/index.html
Chromos - http://www.chromosart.co.uk/
Seawhite - http://www.artesaver.co.uk/
Rosemary Brushes - http://www.rosemaryandco.com/
Artifolk - http://www.artifolk.co.uk/index.htm
Here's some recomendations from Jennie Sendall