Microsoft McLaren leaks out in detail: compared against Apple's iPhone 6
You can also clearly see the label on the device saying it is a 'prototype property of Microsoft Mobile', something that indicates that it is not an old Nokia development.
The most interesting element, however, is without a doubt the large, protruding camera. While we have no way to measure, it seems that the camera hump has grown even larger on the Microsoft McLaren than it is on the Nokia Lumia 1020. Having such a large, but also very noticeable camera is a double-edged sword - image enthusiasts will love it, but those who don't care all that much about the camera will likely find it hard to deal with its bulk on a daily basis.
In either case, it seems that Microsoft is clearly working on the next big thing for Windows Phone, and while this early prototype is no guarantee that it'd look like this, we at least know one of the directions that the company is going to.