The free update to be available in September, is aiming to refine features and styles implemented last year with iOS 8, instead of launching big new features.

The operating system will also take up a smaller amount of space on the device, requiring 1.3GB of free space to install. iOS 8 required more than 4GB to install, which caused issues for users requiring them to delete apps.

Security has been improved in iOS 9 to help fend off hackers. Stronger end-to-end encryption will be used for syncing information such as notes and reminders, while a new set of security extensions will prevent unauthorised access to secure files.

Apple is concentrating on optimising iOS to run smoother and faster with lower power consumption, adding an extra hour to the iPhone's battery life.

An additional low-power mode will add another three hours of iPhone battery life. The new search assistant that is an advance on Apple's Spotlight search facility, integrates with Siri to create a Google Now competitor, capable of displaying data from apps and the web, and controlled via text or voice.