Apple is often accused of deliberately slowing down older iPhones, with conspiracy theorists claiming it is a ruse to force customers to upgrade.

Now, it appears that the theory is true, at least in part. Apple admitted that it deliberately limits the performance of iPhones when a battery ages, to stop them shutting down without warning.

It added the "feature" to the iPhone 6, 6S and SE in 2016 in a software update last year and the iPhone 7 was updated earlier this month, with the release of iOS 11.2. New devices will have their processing power zapped in the future, Apple confirmed.

“Our goal is to deliver the best experience for customers, which includes overall performance and prolonging the life of their devices,” an Apple spokesman said.