thanks for this info

interesting that you are expecting a 50% cost saving on materials
using this stone compared with the readymade moulded concrete version,
but on the pavingexpert.com site i'd noticed it said "...stone paving
is considerably more expensive than the concrete alternatives..."
(http://www.pavingexpert.com/york01.htm)

imported sandstone for about £17 per sq m.
incidentally, how thick is the stone at this price?

You might argue that it's immoral to use a stone which has been quarried in
India and then shipped expensively around the world
(yeah, talking of which, my guess is that the pay & working conditions
of the labourers who quarry that stone in India are worse than
atrocious...)