Amazon’s Prime Day promotion, which kicks off on Monday, has become a red-letter day in the retail calendar. Here we look at the impact of the promotional spectacular and how it has become a consumer phenomenon. 1. Prime Day turns shoppers into subscribers. Prime Day is Amazon’s biggest promotion for customers of its Prime subscription service when the etailer offers its “best annual deals”, backed by free next-day delivery and even delivery within one hour. So popular has Prime become that there are now estimated to be 19m members in the UK. Subscription services, which lock customers in and can generate higher spend as a result, are increasingly common in retail. Prime was one of the pioneers, and Prime Day’s deals hammer home the value on offer to members. See more at Retail Week.