Just to resurrect this ..
I've just use Neills materials as they were the cheapest at the moment for platsil gel 10..cheaper than Dauphines, of which was my go to.
http://www.specialplasters.co.uk
For all my mold stuff. 4D modelshop for Chavant nsp, it's the cheapest if you consider postage.
I recommend Tomps for resin. eBay has some suppliers for rtv silicone.
You will struggle to find brands such as Smooth-on, Monstermakers latex in the UK and you'll never find ultracal 30 anywhere. The best equivalent for ultracal 30 is Crystacast R. You have to find British equivalents but there are plenty of our own brands that are just as good. The only product I can find in abundance that the yanks use is clay, you'll find plenty of Chavant nsp and WED clay. But american molding products are harder to come by.