"Serial returners" who habitually take advantage of free returns by over-ordering are placing increasing pressure on UK retailers, according to a survey by Barclaycard.

The emergence of online shoppers who have no intention of keeping every item is negatively affecting more than half of retailers, with one in five increasing their prices to cover the cost, the study found.

An estimated 30% of shoppers deliberately over-buy and subsequently return unwanted items, the survey found.

Almost six in 10 say a retailer's returns policy influences their decision to buy, and almost half of these would not order an item if they had to pay to send it back.

But almost half of shoppers say that standardising clothing and shoe sizes would save them from having to order multiple items to ensure a correct fit.

Only 18% said a better in-store experience, such as shortened queues for fitting rooms, would reduce the number of returns they make.

The findings come as spending across digital channels rose 14.1% in 2015 compared with just 1.1% in stores.