A quarter of internet shoppers have a next-day delivery subscription, Royal Mail has found, and warned retailers that they must keep up with demand for fast, free delivery to retain their customers.

Of the quarter of online shoppers that do pay for a delivery subscription, 76% are members of Amazon Prime.

The report by the carrier also revealed that online shoppers made 80% of their total purchases on the internet in 2017, excluding groceries.

The figure is a notable rise on the 74% of overall purchases made by online shoppers in 2016.

The research, conducted for Royal Mail’s Delivery Matters report, asked 1,500 UK online shoppers about their internet purchasing habits.

It found that 55% of women who shop online use the internet to buy clothes, spending an average of £40 a month.

Only 33% of male online shoppers use the internet to buy clothes.

Amazon and eBay were found to be the most popular online-only clothes shopping outlets, while of the high street brands, Marks & Spencer and Next make the most online sales.

Royal Mail suggested that more people were spending additional money online because it offered a wider range of choice and convenience.

Nick Landon, MD of Royal Mail Parcels, said: “Despite consumers tightening their purse strings, online shopping continues to grow.

“How you deliver is as important as what you sell and a quarter of shoppers are now paying an upfront fee for unlimited delivery. Businesses of all sizes need to make sure they respond to this demand or risk being left behind.”