A landmark competition lawsuit against US chipmaker Qualcomm is due to begin in London this week, in a case that could see millions of UK smartphone owners receive compensation if successful.

Consumer group Which? has launched the class action on behalf of around 29 million people who bought Apple or Samsung smartphones in the UK. The claim centres on whether Qualcomm used its dominant position in the smartphone technology market to overcharge manufacturers, driving up costs for consumers.

The trial, taking place at the Competition Appeal Tribunal in London, will run for five weeks from 6 October. If Which? succeeds in proving that Qualcomm held market power and breached competition law, a second phase of the case will focus on the company’s conduct and the scale of damages.

Which? estimates that the total amount owed to UK consumers could reach about £480 million, with an average payout of £17 per phone. The group argues that Qualcomm’s licensing and chipset practices allowed it to impose unfair fees on manufacturers such as Apple and Samsung, which were then passed on to customers through higher handset prices or lower-quality devices.

Anabel Hoult, chief executive of Which?, said the case was “a huge moment” for consumer rights in the UK. “It shows how the power of consumers – backed by Which? – can be used to hold the biggest companies to account if they abuse their dominant position,” she said.

“Without Which? bringing this claim on behalf of millions of affected UK consumers, it would simply not be realistic for people to seek damages from the company on an individual basis. That’s why it’s so important that consumers can come together and claim the redress they are entitled to.”

The case marks one of the most significant collective legal actions yet taken under the UK’s competition laws, which were reformed in 2015 to make it easier for consumer groups to bring mass claims.

Qualcomm, which denies wrongdoing, has been approached for comment.