Just placed an order with screwfix, which came to =A345, and a few pence.
Realising that free delivery is for orders over =A350, I was looking around the for something about =A35, which would essentially be free (given the otherwise =A35 delivery charge).
Then I spotted - vouchers, so I added a =A35 voucher, which hey presto takes me above the free delivery threshold, so I get the =A35 to spend next time.