An email sent out to McDonald's customers appears to include a picture of the unreleased iPhone 8, complete with its new edge-to-edge display.

The email, sent to customers in Australia on 18 August, offered a 25% discount on their first order through the fast-food chain's app. But it also featured an image of a smartphone almost identical to recent renders claiming to represent Apple's next iPhone.

Expected to be revealed in September, Apple's new flagship is widely tipped to feature an elongated display stretching to the top and bottom edges. The top of the screen is believed to arc around the phone's centrally-mounted front-face cameras, speaker and a range of sensors.

No official images of the new handset, thought to be called either the iPhone 8 or iPhone Pro, have leaked into the public domain. It is likely that McDonald's wanted to portray a generic smartphone to promote its iOS and Android apps, without seeking clearance from a phone manufacturer to use images of a real product.

But while the user interface has been modified to look generic - the signal strength icon is not from iOS and there is no network name or mention of 3G or Wi-Fi - the bezel, button and mute switch placement, and the display's 'notch' are all from iPhone 8 renders.

The new iPhone's larger display is an answer to the 'Infinity Display' used by Samsung on its Galaxy S8 and S8 Plus. Using this design, the new iPhone will likely have a larger display than the iPhone 7, without an increase in overall size.

Apple is expected to reveal the new handset alongside updated versions of the iPhone 7 and 7 Plus - called the 7S and 7S Plus - at a media event in September.