The news that Amazon might roll out 3,000 of its new Amazon Go shops sent shivers through the US retailing sector last week with CVS, Walgreens, Walmart, Target and Kroger all moving sharply lower. The online retailer plans to have this huge new estate in place as early as 2021, it announced after the launch of its fourth store in Chicago.

After downloading the Amazon Go app, shoppers scan their phone on entering and $1m of modern scanners take care of the rest. Shoppers are automatically charged as they leave the stores that have no checkouts.

So far, Amazon has helped to create all the empty store space it might ever need, but whether it invests the billions needed to deliver on its Go format remains to be seen.