LONDON (Reuters) - A UK tax loophole that benefits foreign e-commerce platforms such as Shein should be closed, the boss of British supermarket Sainsbury's said on Tuesday.

Under UK tax rules, individuals can order parcels worth less than 135 pounds ($170) online from overseas without incurring customs duty. In the EU, the equivalent threshold is a similar 150 euros.

"All retailers should be working on the same basis," Sainsbury's CEO Simon Roberts told reporters after the group, which makes a quarter of its sales in non-food categories, updated on trading.

"I want to make sure that the loopholes that are currently in place are closed for some of the businesses that aren't paying tax in the right way, so it's a level playing field for everybody," he said.

Theo Paphitis, chairman and owner of UK retailers Ryman and Robert Dyas, and Next CEO Simon Wolfson have also called on the UK government to review the loophole.

Shein confidentially filed papers with Britain's markets regulator last month, two sources told Reuters, kicking off the process for a potential London listing later this year.

($1 = 0.7921 pounds)

(Reporting by James Davey; Editing by Sachin Ravikumar)