According to MoneySavingExpert, select Amazon UK accounts are being targeted for an offer whereby you receive a £10 amazon voucher in return for buying £40 of amazon gift cards.
The free voucher would have an expiry of 11th November 2015, however the £40 of gift cards would have the usual 10 year expiry!
This is apparently the link to check if your account qualifies:
https://www.amazon.co.uk/gp/browse.html?node=6969867031&ref=gc_sepb40g10_assoc
If successful you are told what to do on the screen.
If like me you are unsuccessful then it says:
Unfortunately, you are not eligible for this offer.
It seems to be 25 to 50% success rate, so worth trying. No idea if there is a quota to fill before it runs out.