The Hybrid does an average economy of 67.3mpg and emits 109g/km of CO2 in saloon form, while the estate variant manages 64.2mpg and 116g/km.
The Mercedes E300 Bluetec Hybrid achieves these impressive figures with a 201bhp 2.1-litre four-cylinder diesel engine combined with a 27bhp electric motor.
However, these figures are possible only with the no-cost option 16-inch alloy wheels. The standard-fit 17-inch alloys increase emissions to 111g/km and average economy to 65.7mpg for the saloon, while the estate's stats are revised to 119g/km of CO2 and 62.8mpg.
Mercedes says the E-Class hybrid can be driven solely on electric power for up to one kilometre, at up to 21mph.
The electric element of the hybrid system is mounted within the seven-speed automatic transmission to save space. This means the E-Class hybrid has the same boot space and rear passenger room as its conventionally powered counterparts.
In terms of emissions, the E-Class is the most efficient in its class the 2.0-litre diesel Audi A6 manages 129g/km, while the most efficient BMW 5 Series the 520d Efficient Dynamics emits 119g/km. The hybrid-powered BMW ActiveHybrid 5 uses a six-cylinder petrol engine, and emits 149g/km.
Deliveries of the Mercedes E300 Bluetec Hybrid start in November. Prices start at 39,645 for the saloon and 41,435 for the estate.