Apple users get a small amount of free storage, but once that runs out they are encouraged to pay for iCloud to back up photos, videos, messages, contacts and other content from their devices.
Prices range from 99p a month for 50GB to £54.99 a month for 12TB.
Apple does not give rival storage services full access to its devices, saying this is for security reasons – although it also means iCloud has more features than non-Apple alternatives.
Which? claims that since 2015 Apple has effectively locked users into its services and overcharged them as a result.
The consumer group filed its claim against Apple at the Competition Appeal Tribunal on behalf of affected consumers in November 2024.
Anabel Hoult, Which?’s chief executive, said the group wanted to make clear that no company “no matter how powerful, can get away with abusing its position”.
She added the green light from the Competition Appeal Tribunal meant Which? was “one step closer to getting consumers the redress we believe they are owed from Apple”.
“This should send a strong message to any other companies using anti-competitive tactics,” she said.
The case is not expected to be heard until October 2028.