Might the clay product you purchased in the UK be "Nemaslug"???
I found information about it on this site:
http://www.cf.ac.uk/biosi/staf... where it says:
"Since writing this chapter in 1990 there has been a major new development in slug control in the form of the slug parasitic nematode, Phasmarhabditis hermaphrodita. Although I was aware then of work to develop this biological control agent I was not free to make the information public, for reasons of commercial confidentiality. Now, however, these nematodes are available from garden centres under a variety of brand names, including 'Nemaslug'. They come bound up in clay granules, that can be simply dissolved in water and applied to slug-infested crops. Although they do not kill the slugs as rapidly as pellets, infected slugs stop feeding almost immediately and thus stop damaging your crop. The nematodes are completely safe to humans, pests [s/b pets?] and other garden wildlife, including the slug predators. This means, of course, that while slug numbers can build up again rapidly after use of a molluscicide based on methiocarb, because the predators have been removed, after applying the nematodes the predators will remain to prevent slugs re-invading, and to mop up slugs hatching from eggs in the soil."
