Set to be unveiled at the 2015 Frankfurt motor show prior to the start of UK sales at the start of 2016, the reworked roadster sports a number of minor exterior styling tweaks, including a revised front bumper and altered headlights graphics, as part of the mid-life makeover. It is the second revamped Porsche to be spotted testing after the updated 911, which was seen recently.

However, the biggest change looks set to take place in the engine bay, where Porsche is set to introduce a new horizontally opposed four-cylinder powerplant as part of plans to broaden the appeal of both the Boxster and its fixed-roof sister model, the Cayman.

Already confirmed by Porsche chairman Matthias Müller, the new engine is planned to be offered alongside upgraded versions of the existing Boxster’s horizontally opposed six-cylinder engine.

“We will continue with the downsizing strategy and develop a new four-cylinder boxer engine, which will see service in the next-generation Boxster and Cayman,” Müller confirmed last year. “We will not separate ourselves from efforts to reduce CO2”.

When queried on the output of the new four-cylinder boxer engine, Müller said it would produce “up to 400ps [395bhp]”.

Recent information suggests the new flat four engine will range in capacity from 1.6 litres to 2.5 litres, with power otputs from 210bhp through to the 395bhp alluded to by Mueller.

The six-cylinder boxer engine used by the existing Boxster and Cayman develops 261bhp and 271bhp respectively in 2.7-litre form, with a larger 3.4-litre unit offering either 311bhp, 325bhp or 335bhp depending on the model in which it is deployed.