When we road tested the BMW 650i convertible we returned of 28.9mpg on a lengthy run, which may sound thirsty to many, but by the standards of its V8 drop-top peers, many of which struggle to better 25mpg on the run, it is frugal. Emitting 249g/km of CO2, this 6 Series is also £200 cheaper to tax every year than an equivalent Jaguar XK or Mercedes SL500.

Saving around £8000 off the list price and going for the 640i will save you a decent amount at the fuel pumps if the official average figures are anything to go by. The six-cylinder car beats the V8 by 9mpg (35.7mpg versus 26.4mpg), while CO2 drops usefully to 185g/km; that’s a few tax bands, meaning a sizeable company car tax saving of the best part of £300 per month.

Vicky Parrott

Deputy reviews editor
Getting excited with the options list pushes the car's price up rapidly

Likewise, that might make the 640d and its 51.4mpg combined economy and 144g/km figure even more compelling.
 Value seems to speak strongly for the car, too. At well over £70,000, the 650i convertible is still cheaper than the entry-level Porsche 911 cabriolet – undercut only by Jaguar’s 5.0-litre XK – and comes with 19in alloy wheels, Dakota leather upholstery and a 10.2in sat-nav system.

Just beware the options list, because a fully loaded 650i with Adaptive Drive, Integral Active Steering, a head-up display and all of the other toys will cost you more than £94k.

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The 640i and 640d already come nicely equipped with more acronyms than you could possibly imagine and a decent roster of luxury equipment, too. Once again, though, BMW dealers will do their utmost to get you to plunder the options list, which can affect not only the amount you pay for the car, but also the rate of company car tax.

For the more family-oriented, the Gran Coupe would make for an ideal company car purchase (as it shares its low running costs with the standard coupe) but for its high asking price when compared to its rivals. An Audi A7, for example, matches the 640d's 309bhp and can be bought from £46,120. A 640d SE is £63,900.Moreover, the M6 flagship, despite its crushing performance, also appears poor value. Put simply, the M5 on which it is based offers identical power in a more practical bodyshell for £20,000 less.

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