The voucher was pulled by eBay, the story circulating is that it was intended only for the use of the few that received the original email. But they chose a generic voucher code rather than a recipient unique code, and once it hit social media, the national press, HDUK, etc. it went viral and they lost control.
Sometime early in the afternoon it stopped being accepted. I gather it's upset a few people that placed orders and expected the discount to be retrospective even after they had the error message saying there were no funds remaining.