Amazon is facing a one billion-pound ($1.3 billion) collective lawsuit from British retailers who allege that the online marketplace misused their data to boost its own market share and profits.

The British Independent Retailers Association (BIRA), an umbrella body grouping numerous small traders, was due to file the lawsuit on behalf of around 35,000 retailers at the Competition Appeal Tribunal (CAT) in London on Thursday, its lawyers said.

The suit alleges that Amazon made use of non-public data provided by retailers selling goods on Amazon's Marketplace to offer cheaper rival products for sale directly to consumers.

BIRA Chief Executive Andrew Goodacre said small retailers had little choice but to use Amazon, given its reach, but that the case was intended to stop it putting them out of business.

"The filing of the claim today is the first step towards retailers obtaining compensation for what Amazon has done," Goodacre said in a statement.

Amazon did not immediately respond to a request for comment.

BIRA's case also alleges that Amazon manipulated the "Buy Box" feature on its website, shown near the top of product pages, to its own advantage.

The "Buy Box" is the subject of a separate lawsuit brought on behalf of consumers and valued at up to 900 million pounds ($1.1 billion).

Britain's Competition and Markets Authority (CMA) said in 2022 that it was investigating Amazon, including the way it selects the products placed within the "Buy Box".

Last year, the CMA said it had accepted commitments from Amazon to help protect fair competition on its retail platform.

(Reporting by Sam Tobin; Editing by Kevin Liffey)