For Lexus, it’s been a valuable development. The CT 200h arrived as a competitive premium C-segment rival in 2011, and the four-cylinder IS 300h finally made large hybrids a viable proposition against the default diesel engine last year, while stealing a lead on CO2 emissions as it did so.

The GS 300h takes that challenge further. It’s the first four-cylinder engine ever to feature in Lexus’s full-size executive car, which means it has its work cut out taking sales from the ubiquitous BMW 520d and a crop of excellent diesel options available from its German rivals.

Though it’s a latecomer, it’s making a strong entrance on paper. Fuel economy of 60.1mpg for the SE trim tested here equate to 109g/km CO2 emissions, which put this car neck and neck with the revised 520d and within reach of the diesel-hybrid E-Class. Pricing is competitive and the combined 217bhp from the electric motor and 2.5-litre petrol engine should be attractive, too.

But hybrids don't always work in bigger cars. Springy CVT gearboxes can blunt the power delivery and the drone and thirst of a hard-working four-cylinder engine under load are unappealing qualities in a car like this. Cast those doubts aside, though. Somehow, Lexus has managed to avoid all of these in the GS 300h.

Actually, it’s a surprisingly good fit. The GS 300h is almost silent even with the petrol engine running, quieter even than the GS 450h, while delivering a smooth waft of power for effortless, relaxed on long distance driving. The engine switches off altogether at low loads, which is surprisingly often in town, saving fuel and gliding along silently on its electric motor.

If anything, the 300h drivetrain suits the GS better than the IS, which felt like it needed an extra shove of urgency to go with its low driving position and sporty styling.

Ride quality is fantastic in SE spec, the GS taking the thump out of even the roughest roads and adding to the overall feeling of calm created by the drivetrain. Material quality – particularly the leather upholstery – is generally very high, and the seats strike a good balance between being supportive yet soft enough to be very comfortable.

Most importantly, though, fuel economy figures which easily settle at around 50mpg on a motorway run shouldn't blunt that sense of relaxation when flicking through the trip computer screens.

However, despite the aggressive-looking F-Sport trim offered higher up the range, the GS is more of a long-distance cruiser than a driver’s car, and some may miss the directness offered by a German diesel saloon. Lexus’s haptic touch infotainment system isn’t as intuitive as rivals’ equivalents, either, particularly when dealing with navigation functions.

There’s also a packaging sacrifice. The battery, located behind the rear bench, reduces boot volume by a sixth and stops the bench itself from folding flat. The remaining luggage area is still large, but more suited to golf clubs than suitcases. Unlike BMW, Audi or Mercedes-Benz, there’s no estate version, nor could there ever be with the battery as it is.

Ultimately, though, the GS 300h is a proof of concept for Lexus, showing that a German diesel saloon needn’t be the only realistic option in this class.  

Verdict:

The GS 300h isn’t as focused to drive as a 520d, but that isn't necessarily a negative point. By no means short on performance or fuel economy, and perfectly suited to this relaxed executive car, the four-cylinder option makes the GS a very appealing option in the executive class.

Specification:

Segment: Executive

Type: Petrol-electric hybrid

Price: £33,490

Fuel: 60.1mpg

Electric range: 1 mile

CO2 emissions (tailpipe): 109g/km

Charging port: N/A