A consumer champion is suing Apple for £768m over a software update in 2017 that effectively slowed down older iPhones.

Justin Gutmann is seeking damages on behalf of up to 25 million iPhone owners in the UK who were affected by Apple's practices.

Apple has admitted that a software update released in 2017 hampered the performance of devices, although it claims the software was meant to protect the phone's battery life.

Critics have accused the company of purposefully reducing the effectiveness of older models to push customers towards buying newer ones.

The company previously paid $113m to settle a similar case in Arizona, and $500m to settle another in California.

Mr Gutmann's claim has been filed with the Competition Appeal Tribunal, the UK's specialist judicial body that hears cases relating to anti-competitive market practices.

It is an opt-out claim - meaning people who owned an iPhone 6, 6 Plus, 6S, 6S Plus, SE, 7, 7 Plus, 8, 8 Plus and iPhone X model do not need to actively join the case to seek damages.

"Instead of doing the honourable and legal thing by their customers and offering a free replacement, repair service or compensation, Apple instead misled people by concealing a tool in software updates that slowed their devices by up to 58%," Mr Gutmann said.

"I'm launching this case so that millions of iPhone users across the UK will receive redress for the harm suffered by Apple's actions.

"If this case is successful, I hope dominant companies will re-evaluate their business models and refrain from this kind of conduct," he added.

The scandal erupted following a study by a Reddit user who claimed that Apple's tech automatically slowed phones when the battery has a diminished charge capacity.

Apple admitted causing the issue and apologised for the apparent downgrade.

In a statement, the company explained that as the lithium-ion batteries used in its phones age they become less able to provide the top levels of electrical current needed.

The problems with peak current draws especially occur when batteries are cold or low on charge - "which can result in the device unexpectedly shutting down to protect its electronic components", Apple said.

Lithium-ion batteries lose their capacity over time due to the physical wear-and-tear of ions passing through the material of the battery.

But iPhone users had complained about their devices turning off abruptly even when they had a significant amount of charge left.

The company eventually said it would be replacing users' batteries for a discounted rate for a limited time and also introduce a feature to allow users to turn off the power management tool.

The company said it had never and would never do anything to intentionally shorten the lifetime of a product. Its chief executive Tim Cook publicly apologised and said Apple has not tried to mislead anyone with the software.

However Mr Gutmann claims Apple did not do enough to inform customers about its battery replacement service and that the company has abused its market dominance.

Apple has not commented on the new legal claim.