Petrol power, diesel economy from Merc - Introduction

One of the stars on the Mercedes stand at the Frankfurt Motor Show last year was its F700 concept car.

It had a range of new technologies that Mercedes expects will work their way into its production cars over the coming years, the most significant of which is its Diesotto engine.

This is a petrol engine that behaves - at least some of the time - like a diesel engine, combining the power of a petrol unit with the pulling power, fuel-efficiency and low carbon dioxide emissions of a diesel one.

Getting the engine into a production car is still some way off, but we've been a passenger in the F700 and were impressed.

Here's why...