I'm a fan of Tuffnell's own brand:
http://www.tuffnellglass.com/content...d_Release.html
It's a powder, you can just mix it up as you need it. A pack costs £8 and lasts for a very long time. It holds well but is easy to clean off the mandrel afterwards.
Or they can sell you two small tubs of Fusion for £5. Plus post of course.