Is this a new McLaren that's powered by an ion engine? Perhaps it burns refined goat milk rather than gas? The reality is likely far less spectacular. The XP2R is almost certainly the testbed for a more potent version of the already freakishly quick McLaren P1, or perhaps even a prototype of an upcoming endurance car to take the place of the 12C racer.
We're leaning towards the former rather than the latter, simply due to the seeming lack of racing-specific bits. The windows look like glass, rather than Lexan, and the aerodynamics package looks too close to stock to be for racing. There's also no evidence of racing-spec safety features in the cabin, although it's difficult to tell for certain from these images.
Or maybe McLaren just trotted out an old prototype of the P1 so we'd jump all over it and some engineers in the UK could have a laugh. Whatever the XP2R is, we're keeping our ears to the ground for any additional info and we'll be sure to update you as soon as possible.