In fact, the E300 is unlikely to undermine the four-cylinder diesel E-Classes, because it's expected to carry a price premium over the E200, E220 and E250 models. Instead we're looking at an alternative to the E350 CDI, and a potentially worthwhile one at that.
The E300 blends Merc's 2.2-litre, 201bhp four-cylinder turbodiesel with a seven-speed automatic transmission and an integrated electric motor. It's capable of 67mpg, Merc says, and will emit just 109g/km of CO2 that's the same figure as the 520d Efficient Dynamics, although the E300 does it with an auto 'box. BMW's star uses a six-speed manual transmission. The E300's performance seems strong, too; it'll crack 150mph and reach 62mph in 7.5 seconds.
It's due on sale in July, and is expected to cost around 38,000. That's almost 10k more than an E250, but crucially, around the same as a well-specced E350 CDI. Given that the six-cylinder diesel model emits 162g/km of CO2, the E300 Hybrid is going to look a strong proposition against it.