Twin test: Mercedes E 300 de vs Mercedes E 300 e

You know the old ‘apples and oranges’ analogy? Well, it doesn’t apply here. We’re definitely comparing apples with apples or, in fact, Mercedes E-Class with Mercedes E-Class. Both are plug-in hybrids, with a 13.5kWh battery that delivers an electric range of 31 miles. Both have a 2.0-litre engine, nine-speed auto gearbox and rear-wheel drive, and they cost within a few hundred quid of each other. The difference? One is diesel and the other is petrol.

Mercedes is the only manufacturer to offer diesel plug-in hybrids (PHEVs) and the benefits are clear. Most petrol PHEVs manage mid-30mpg in real-world use once the battery runs out, but a diesel promises more like 50mpg. Makes sense, right? Especially for high-mileage business users.

But there are various reasons, from air-quality concerns to fear of tax penalties, that you might avoid diesel. Which is why we’ve put these two cars back-to-back: to find out just how a hybrid diesel stacks up next to its petrol-powered twin.

Mercedes E 300 e AMG Line Premium

Pros: Supremely smooth and quiet, with similar fuel economy to rivals

Cons: Both diesel and petrol lose significant boot space to the battery

Mercedes E 300 de AMG Line Premium

Pros: Decent real-world fuel economy and very quiet by diesel standards

Cons: Costlier insurance and depreciation, and uncertainty over future legislation

Read on for our full in-depth comparison of these two plug-in hybrid Mercedes E-Class models...