A quick search of the UK government database reveals that this "Porsche" is actually registered to Bentley, and features a 4.0-litre petrol engine under the bonnet.
This prototype is most likely powered by a version of Porsche's new 4.0-litre twin-turbo direct-injection V8, which made its debut along with the second-generation Panamera. In the Porsche, this motor develops 404kW of power and 770Nm of torque.
Aside from being a nifty disguise, the new Bentley Flying Spur is able to easily don the Panamera's body because the two cars share Porsche's newly developed MSB component set for front-engine, rear- and all-wheel drive cars.
The only visible alteration to the Panamera's body are slight wheel arch extensions at both ends, suggesting that the new Flying Spur will feature dimensions roughly similar to the Porsche, which is 5049mm long, 1937mm wide and 1423mm tall. Unlike the Panamera, the Flying Spur should be a traditional three-box sedan.
MSB will also be used underneath the next generation versions of the Bentley Continental coupe and convertible. Both the coupe and convertible have already been spied wearing near-production body parts, albeit with the healthy assortment of false panels.
As the two-door Continental models are expected to launch in the second half of 2017, it's safe to assume that the Flying Spur sedan will follow on from those two cars, probably some time in 2018.
The switch from the current cars' front- and all-wheel drive platform, shared with the Volkswagen Phaeton, should do wonders not just for the new Continental and Flying Spur's proportions, but also their weight and fuel economy.