The petrol ones are the cheapest to insure, with 1.1-litre petrol VT models rated at just group 5. Diesel models occupy relatively low groups too, with most sitting below group 10. In fact, you'd be hard pressed to find a diesel car with a lower insurance group than that. Combined economy is 64.2mpg on a 1.4-litre HDi VT model (insurance group 8).