I gave this a whirl this morning, as I needed to stock up on cleaning products, after a horrible experience with a washing machine, delinquent cat, a semi boiled mouse and assortment of child's clothing, which I won't explain in detail, as you may well lose your lunch, but was enough for me to buy every washing machine cleaning agent, that I could from Amazon Prime Now!
I selected £50 of goods from Prime Now, entered the promo code of BACK10, and indeed a £10 promo discount was deducted from my bill. I also got a free 2 hour delivery slot, as my order was over £40, so all in all, this was a pretty good deal!
The deal is live until 31st January 2020, so you do have plenty of time to take advantage, but there are a few exclusions and terms and conditions, (I have copied these below for you).
If you are interested in earning some extra cash, delivering for Amazon, you can sign up via the Amazon Flex programme, and earn yourself £14 per hour.