Hybrids in fuel economy blow

New fuel economy rules are set to have a crippling effect on hybrid mpg figures.

Until now, testers have classified plug-in models as all-electric – so only their battery power has been assessed, producing inflated economy figures. But the United Nations argues that as the cars switch to fuel once the battery is flat, those emissions should also be included in the calculation.

The loophole has now been closed in the UK, however – so cars such as the forthcoming electric Toyota Prius will get their own test. A spokesman for the Society of Motor Manufacturers and Traders (SMMT) told us: “The United Nations has come up with a system for the UK where hybrids are tested once when the battery is full, and again when it is empty and the engine is running.”

General Motors says the method of testing is also being reviewed in the US – where the Chevrolet Volt has a rating of 100mpg. The Volt, due here in 2011, is an electric vehicle with a range-extending petrol back-up generator. So its economy figures are sure to be slashed if the proposals get the go-ahead.

But a GM spokesman argued: “Volt customers who drive to work or to the shops may never use the petrol engine. How do you create a test that truly represents their economy?”