After much persistence I tried with my works email address and the email came through pretty much straight away.
FWIW - Looks like the code you type in is not unique to each 15 pack as I bought 2 packs the other day and both have the same code on the bottom of the pack.
Now to try and see if my email hosting company is on some sort of blacklist. Definitely not my local IP as I've not received the mails when confirming details on my PC using PlusNet or using my 4G on my phone - unless there is some BT issue here as they are both owned by BT.
Ah well, at least I have one glass coming soon. Will go for more though as it's one per person per household so I can claim 5 in theory.....