What will they cost?

Back in 2012, when both cars were new, the 640d cost slightly more than the XK and, on top of that, there was more chance of getting money off the Jag new than the Beemer. However, it’s interesting to note that, at this age point, the Jaguar has held on to slightly more of its money than the BMW. You can pick up a good, clean example of the 640d in M Sport trim for around £22,000, which seems very good value for such a premium product.

By contrast, the XK, in 5.0-litre V8 form, would set you back nearer £30,000 for a car in the same condition, with a full history, an average mileage for the year and bought from an independent dealer. Initially, the 640d would have been expected to hold on to its value better, so could this be an indication of a fall in demand for diesel-engined cars, even in this exalted sector?

In terms of economy, the BMW has the Jag licked. The sheer size of the 640d’s advantage may come as a shock, though; its average claimed fuel consumption figure is 51.4mpg compared with the XK’s paltry 25.2mpg. What’s more, it means the 640d can cover a whopping 791 miles between fuel stops – 400 miles more than the XK. That’s pretty remarkable. Fuel economy and CO2 emissions go hand in hand, of course, so the 640d will also save you a good deal of money every year in road tax.

The BMW has variable servicing periods and main dealers will offer a form of used car servicing plan to cover newer models bought from them. There are also a number of specialist independent firms that will service your car at a reduced cost. The Jaguar requires servicing every 15,000 miles and, likewise, there are a number of independent agents that will take on that task at slightly less cost than is likely to be charged by a main dealer.

In terms of reliability, both cars score well. BMW build quality is decent and the 6 Series has a good reputation for reliability, doing better than most other BMW models in our most recent survey. Jaguar has made great improvements in this area in recent years and the firm continues to score highly in customer satisfaction surveys, and reported problems with the XK are few.