We now stock the excellent Aves Apoxie Sculpt: This is an American-brand 2-part epoxy that falls somewhere between ProCreate and Milliput in terms of feel and use.
We use it extensively for scenery, filling in gaps on figures, sculpting small parts such as sandbags, walls, tree stumps, zimmerit on tanks, waves on water and so on and so forth. We also use it for skinning styrofoam to make large volume masters, such as the hull of our Grav Tank prototype.
Aves Apoxie is a favorite of starship modelers, and - if you pop over to the Starship Modeler forums - you will find lots of reviews and help on how to use it.
We have not used this for figure sculpting ourselves, so your mileage with it in that field is unknown, I'm afraid.
All the same, we heartily recommend it as it dries rigid, can be sanded (without clogging your sandpaper), can be drilled, is waterproof when dry, but before set can be cleaned up with water.
We stock a huge 1-lb set which retails at £12.99 GBP; a smaller 2oz set for £5.85 GBP; and the Aves Safety Solvent (4 fl oz), which is excellent for cleaning up from tools, brushes and so forth, and works well on other putties of a similar nature - the solvent sells for £15.99 GBP, and should last you a very long time!
We hope to be stocking the new Aves Apoxie Paste later in the year - that being a semi-liquid paste that makes skinning styrofoam shapes even easier.