Customers of online retailer Amazon are now required to spend a minimum of £20 to qualify for the website’s free ‘super saver’ delivery service, double the original spend, in a move widely seen as pushing customers towards its Prime next day delivery subscription service.

The site introduced the £10 minimum spend in 2013, which still applies to book purchases.

The US company has invested more than $1.3bn, in an effort to boost the attraction of its Prime membership. Streamed movies, TV shows and other bundled content have been added to the service, benefits that the company’s chief financial officer, Tom Szkutak, says are “certainly impacting our operating results, but we like what we see”.