Posted: 21/12/2016 at 20:33
Just checked the RHS site:
and that says it is glyphosate based, which is good news as that is inactivated when in contact with soil, so won't have affected the hedge by percolating through the slabs into the roots. The only way glyphosate based weedkiller could have affected the hedge is if the spray was blown onto the leaves of the hedge by wind. Is that a possibility? Even if it is, the hedge may only have been weakened and may well survive and green-up in spring.