Sainsbury's is planning to punish customers for shopping at other supermarkets through a major change to its Nectar card.

The supermarket is trialing an overhaul of the system where customers no longer receive a point for each pound spent, but instead receive larger rewards the more they shop at Sainsbury's.

It comes amid a growing trend in which millions of loyal supermarket shoppers are straying to Aldi and Lidl to take advantage of bargains, hurting mainstream retailers' profit margins.

Sainsbury's will run the trial across all of its stores on the Isle of Wight from April 12.

It says it aims to give loyal Sainsbury's customers more points, meaning those who shop at a range of stores may lose out.

Under the trial customers will be offered access to a new app which will show customers individual offers based on their previous shops.