Convention would suggest that the lowest BMW 2 Series Convertible running costs would come from the diesel-powered model but, while that may be the case in reality, on paper the new three-cylinder 218i petrol runs it close.

Emissions of this 1.5-litre petrol engine mated to the eight-speed automatic are just 131g/km, so annual VED car tax is reasonable. Consider too the 50mpg combined economy, and the £57 fill of the 52-litre tank (at time of writing) promises a 571 miles range.

The 220d, with the same gearbox, emits 117g/km and will cost £60 for a full tank covering 161 miles extra per fill. Cheaper per mile, but nearly £3,000 more expensive to buy in the first place – you’ll need to travel 141,000 miles in the 220d to make up the price difference with your greater economy.

Clearly the most expensive 2 Series convertible when it comes to running costs is the M235i, as much for fuel and tax costs as for tyre and brake replacement. All are eligible for the firm’s Service Inclusive, and Service Inclusive Plus, packages though so you can regulate how much you’ll spend on maintenance over the course of five years – and pass on the benefit to anyone you sell the car to within that time frame.

At launch BMW 2 Series Convertible emissions are taken care of by four engines – the 220i, 228i and M235i petrols and one diesel, the 220d. Later in 2015 we’ll see the introduction of the three-cylinder 218i.

But regardless of which model you choose, the BMW 2 Series Convertible is pleasingly efficient. Even the M235i, the most polluting of the range, only pumps out 199g/km of CO2 (184g/km for the automatic gearbox). And all come with start/stop systems and the firm’s Driver Performance Control including ECO Pro mode with hints, tips and altered parameters for the most efficient driving.

It’s the 220d that is the most impressive in this department though, with its two-litre four-cylinder diesel engine producing 188bhp, taking just 7.5 seconds to spring from 0-62mph and emitting just 121g/km. Choose the eight-speed automatic gearbox and that drops to 113g/km, while the 0-62mph time is improved by one tenth of a second.

Much of the engines are used elsewhere in the range so we’d expect in the main that BMW 2 Series Convertible reliability will be very good. Certainly, there’s no reports of any problems with the drivetrains used anywhere else and we’d expect the car to continue the firm’s good reputation for reliability.

The roof is excellently engineered too, and there’s little shake through the car’s structure when it is being opened or closed – even when on the move. Plenty of insulation, and the resulting lack of external noise on the move, points to it being a quality item too.

Choose the colour of your cabin wisely though, as lighter leather colours won’t wear as well as the darker tones. At least each features a dashboard and switchgear that are robust and, like the Coupe, will likely stand-up to the rigours of daily life.