Wickes have several that have no fixing holes in the cistern, which infers the above... However, they have a flush valve I have never seen before:
After much Googling, it looks like a Geberit style.
Are these things actually sort of standard, or would I be shooting my feet off choosing a cistern with one in? It seems quite hard to find spares, but maybe I am Googling for the wrong search term...
The do seem quite elegant - no pipe or cable to stop the lid being removed, otherwise a standard close coupled cistern.