What real-world fuel economy should you expect from a petrol hybrid like the Lexus IS 300h?

I feel that 20mpg below the official figure is disappointing.

But reader Rob Chisholm, from Applewood Vehicle Finance, has given me food for thought.

He suggests that 45.3mpg (the fuel economy I was achieving at the time of my last report in February) isn’t a poor return, considering that the IS 300h runs cheaper fuel than its rivals (petrol is currently around seven pence a litre less than diesel). 

He has a point, particularly as the price of petrol has just fallen to a three-year low.

His comment prompted me to look at the official figures of the IS 300h’s key diesel rivals.

The Mercedes-Benz C250 CDI AMG Sport auto, for example, quotes 56.5mpg. That’s nearly 10mpg below the IS 300h’s 65.7mpg and the C-Class’s power output of 204bhp isn’t far off the Lexus’ combined output.

The BMW 3 Series also doesn’t match the IS 300h. The 325d SE auto has a combined figure of 61.4mpg, although it is more powerful than the IS 300h and the C250 with 215hp.

Bear in mind that both the C-Class and the 3 Series will attract a 3% benefit-in-kind diesel supplement. Their higher CO2 emissions will have an impact on personal taxation and the employers’ National Insurance Contribution too.

So perhaps I am being too harsh on the Lexus.

It’s also worth pointing out that my daily commute is mostly on the A1 – not the ideal type of road for a hybrid, which are better suited to urban environments.

Magazine What Car? drove more than 160 new cars in 2013 to capture true fuel economy data and they achieved 59.6mpg in the Lexus IS 300h.

That’s 13mpg more than I’m achieving and shows that I should expect better.