Jackie Stewart is talking as he drives: fast, smooth and confident. As the new long-wheelbase Jaguar XJ sweeps up Highway One north of San Francisco, today’s subjects are car development engineers and his current problem.

‘For the first time in 40 years, I might have to buy a car,’ Stewart muses. For the last 25 of these, the only Briton to have won three F1 world championships has travelled almost exclusively in the back.

‘The problem,’ he continues, an evangelical note creeping into his inimitable Scots accent, ‘is that cars are almost entirely developed from the front seat, and the difference in ride and refinement from front to rear can be huge.’

Now, Stewart is one of the most professional people you could ever meet and, for the purposes of this exercise it is Ford, through Jaguar, which is paying his fee for carting us up the California coast.

So it should be no surprise that he continues to extol the virtues of life in the back of the longer XJ over the Audi A8, BMW 7-series and Mercedes S-class, all of which he is intimately acquainted with.

Sitting in the back of the Jag, my feelings are mixed. Certainly the ride is close to sublime – compliant but not soggy – in a way that lets you feel connected to the ground but not subject to its many and various imperfections.