A number of high-mileage journeys have highlighted some of our long-term Ampera’s strengths and weaknesses.

Its strengths include the ride, handling, quiet cruising and very comfortable cabin, which is suited to long journeys.

The weaknesses relate to the cars design for a particular operational cycle.

With our Ampera’s battery offering an average of 30 miles on a single charge, the car very quickly switches over onto petrol power on long journeys.

It doesn’t take many miles for the fuel use to eat into the 250+ mpg achieved while running on electricity and the economy figures continue falling until you can plug in again.

Over less than 100 miles, it will still return healthy 100mpg plus figures, but it will fall to about 55mpg on very long journeys.

Such long runs have given me the chance to assess fuel economy when running on petrol power and the Ampera averages about 40mpg, which is still a healthy real world that matches other petrol engines.

However, the combined effect of these longer journeys is a substantial dip in the Ampera’s overall fuel economy, to a still impressive 126mpg over the past 3,000 miles (135mpg over its 13,000 mile lifetime).

When running on petrol, the Ampera costs 14.7 pence per mile in fuel, compared to 3ppm on electricity, so it pays to plug in whenever you can.

Over the past 3,000 miles of testing, our Ampera has covered roughly two-thirds of that distance on electricity.

The total cost of petrol to cover 1,000 miles is around £148. To cover 2,000 miles using electricity has cost just £60.

However, this does highlight an interesting point. As the Ampera is ideal for shorter journeys, the opportunities to reduce fuel costs are limited.

If the Ampera covered 40,000 miles over four years and two-thirds of that was on battery power, it would cost £2,769 in petrol and electricity charges.

A diesel achieving 55mpg would cost £4,558 in fuel costs over the same distance, representing a £1,789 fuel saving for the Ampera.

It still represents a substantial reduction in cost compared to the diesel, but fleets will need a clear idea of mileage patterns and how much time drivers will spend on battery power before they know the fuel savings the Ampera will generate for them.