I used to use Evans anti-slip but they stopped selling it as such, probably in case they were liable for any slips!!
Solutions were marketing a non-slip polish a couple of years ago, it was used in the Eden Project and Hong Kong Airport. As far as I know it is / was the only true non-slip polish around. Don't know if they still sell it.
If anyone knows where to get any other non-slip I'd be interested too.