We’ve gone on at length about how good the M-sport styling kit – larger wheels, deeper bumpers, side skirts – looks on our long-term BMW 5-series, but the other thing that makes it look the part is the optional Carbon Black paintwork.

It costs a fairly average (for metallic paint) £640, and when clean it has an almost blue twinkle to it. But here’s the rub (as anyone who’s owned a black car will tell you): they’re hell to keep clean.

You can wash the car on Sunday afternoon, but by the time the dew (or rather the frost) has evaporated on Monday morning, the residue left by that moisture has taken off the shine.

So when the people at Turtle Wax asked if we wanted to try their new cleaning kit just for black cars we leapt at the chance.

Costing £25, you get a set of cloths, polishes and waxes to keep your car shining for longer. It also helps remove the tiny scratches that show-up on black cars more than others.

Our decidedly unscientific test found it to be great, but you did have to put a lot of effort in. However, the pay off was the car did seem to shine for longer in the winter grime than it does following my usual simple wash.

BMW 520d Touring M-sport
Business Edition 5dr auto
Mileage 8109
Claimed combined consumption 48.7mpg
Our average consumption 38.3mpg
P11D price £34,790
Model price range £31,090-£67,905
CO2 (tax) 154g/km (21%)
BIK 20/40% per month £121/£243
Service interval variable
Insurance group 16
Warranty 3yrs/unlimited
Boot space (min/max) 500/1650 litres
Engine size/power 1995cc/177PS
Top speed/0-62mph 139mph/8.6secs
Why we’re running it To see if 520d Business
Edition can match rivals
Positive Excellent efficiency,
great to drive, classy
Negative Short life brake pads,