It looks like Amazon has launched a new service called Hub. From the description, it’s basically a click & collect service where you can pick up your order from a locker or counter at various locations, instead of ordering delivery.
To encourage customers to try it out, Amazon is offering a new incentive: the first 9,000 eligible customers will receive a £5 coupon code after using Amazon Hub for the first time by 11 August. The minimum order value is £20.
The promotion page is here. No sign-up is needed, and you should see whether you are eligible by visiting the page.