If you receive a Wiggle E-Voucher, and also use the free delivery service, be sure to select your delivery method BEFORE entering your voucher code otherwise you will NOT receive the discount.
I've just experimented with the website and it does tell you to do this, but I didn't notice two days ago and got caught out.
(Unless the warning has only been placed there in response to complaints?) -- Amazon: "If you are interested in 'Asimov's I-Robot', you may also be interested in 'Garfield - The Movie'. ... erm, how do they figure that one out?