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Trying to keep a cutting-edge new gadget under wraps is getting harder and harder. And it doesn't help when a massive UK retailer accidentally spills the beans.

Carphone Warehouse has revealed almost all the details of the forthcoming Google Pixel phone a day before the company was scheduled to announce it.

The US tech giant has been building momentum for an event on October 4 for a few weeks now - but it appears to have fallen at the final hurdle.

The finished pictures show the phone from both sides as well as listing some of its key features. The white gadget bears a striking resemblance to the iPhone 6 although it has the rear-mounted fingerprint scanner popular with other Android handsets.

Both the smaller Pixel and the larger Pixel XL will make the jump to the USB-C charging port and both will have 4GB of RAM and the same 12MP camera on the back (8MP on the front). There will be a choice of either 32GB or 128GB of internal storage.

According to the Carphone Warehouse listings, Google will be offering unlimited amounts of photo storage through its Google Photos app. The latest version of Android (Nougat) is pre-installed and with that comes Google's AI-powered assistant Allo and the FaceTime-style app Duo.

It also revealed new Live Cases - basically covers for the phone that match with live wallpapers you can install.

Differences between the two phones come down to things like size, screen resolution and battery power. The Pixel has a 5-inch, 1080p screen with a 2,770mAh battery whilst the Pixel XL offers a 5.5-inch, 1440p screen with a 3,450mAh battery.

For comparison, Apple's iPhone 7 has a 4.7-inch screen with a 750p display and a 1,960mAh battery, while the iPhone 7 Plus offers a 5.5-inch screen with a 1080p display and a 2,900mAh battery.

In fact, the only thing that wasn't revealed about the two new phones was their pricing and availability.

Google is also heavily expected to reveal some other hardware at its event tomorrow, including a competitor to Amazon's smart Echo speaker .