Kindle Daily Deal - Check Your Receipts
This morning I received a receipt email for £6.26.
I can't believe that Amazon do not drive the price shown on the page and the price charged from the same database record, so I suspect this was a distributed database update problem. So the takeaway is if you purchase from Amazon very soon after a price change - check your receipt.
No doubt Amazon Customer Services will see me right, but I wonder what would have happened if I hadn't noticed.