McLaren Prototype spotted over the weekend in Hampshire

[Trevatanus]

A couple of colleagues spotted a Proto-type testing over the weekend, one driving around Lasham Airfield and the other going through Hook.
Apparently it's a 21st Century reboot of a Can-Am, ie a convertible racer.
Anyone know what it might have been?

[isaldiri]

Mule for a possible (probable?) convertible P15 or perhaps some one off customer MSO special.