The 2.0-litre diesel engine, launched a couple of years ago under Vauxhall’s optimistic Whisper branding, is a known quantity.

With 295lb ft between 1750rpm and 2500rpm, it delivers a credible amount of shove through the mid-range – enough, one would think, to easily distinguish it from the 60lb ft less put out by the 1.6-litre diesel.

Car’s mass and relatively soft springing make it feel a bit unwilling to turn in to quicker corners

Unlike that engine, the bigger unit features a two-stage turbocharger rather than variable geometry, and its response is generally very decent.

Somewhat less convincing is the level of refinement. Despite its protestations, Vauxhall’s common-rail 2.0-litre diesel has never been particularly hushed and its dull-edged but distinctive rumble carries over.

Much of the familiar resonance is segregated by low crank speeds, making its most productive phases and cruising speed volume mostly acceptable.

Stray beyond the margins, though, and you’ll find a strained, old-fashioned clatter that Vauxhall’s premium-end rivals have started to damp out.

The same manufacturers have also become better at making the performance of their four-cylinder engines seem less noticeably tapered.

The Insignia revs to 5000rpm, but there’s a dwindling of productivity from 3750rpm onwards. That’s forgivable in a smaller diesel motor but less so in a unit that’s intended to compete with the increasingly punchy, freer-spinning oil-burners that all develop beyond 150bhp.

Even with a burly diesel engine over the nose, the Insignia’s weight loss is palpable, though – less in the margins that make up its mildly enhanced 0-60mph time (a few tenths of a second, according to our 8.7sec measure) and more in the slightly liberated way it gets under way for such a large car.

It’s a subtle gain perhaps, yet, like the driving position, it permeates the experience from behind the wheel with a wider sense of amenability. In a car intended to function as a mobile workspace, that upshot repeatedly pays dividends. 

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