IF THERE were to be a lonely hearts column for cars, the newest arrival on the scene might sum itself up like this: “Has a reputation for luxury travel, enjoys the fast life (125mph) but is amazingly frugal (50.3mpg). GSOH (good sense of handling), quiet and unobtrusive, described by some as a good looker. Seeks credibility but can be very late for parties. Reply Box X.”

Unlike those lonely hearts ads, there is no secrecy about its name. For the above refers to the Jaguar X-Type . . . diesel. At long last, Jaguar has arrived at the diesel party after Mercedes-Benz, BMW, Audi and even Alfa Romeo have shown how they can play high numbers with both mpg and mph and still have a sporty, enjoyable car that makes them lots of money — and lots of customers happy.

But now the Jaguar diesel is arriving, albeit with a certain coyness and caution not wholly in keeping with Jaguar’s image for thrusting technology, and not until September.

The X-Type diesel’s engine is the turbocharged 2-litre used to power the Ford Mondeo and the gearbox has only five speeds, yet six are de rigueur these days in the premium diesel sector. While other Jaguar models have six-speed automatics, there is not even an automatic option for the diesel X-Type, even though diesels and autos go well together.

But Jaguar is in modesty mode. It is happy just to have gained admission to the diesel party and it wants to ensure that everything is just right before progressing (there will be a V6 diesel S-Type next year and a diesel XJ later).

Certainly the X-Type diesel is at or near the top of its class in terms of performance, economy and emissions. And the company has used its fine engineering expertise to make the 128bhp diesel sound on the move almost like a Jaguar petrol engine, purring quietly even when cruising quickly but giving a modest growl when roused. Impressive.

Performance is reasonable, with nought to 60mph taking 9.5sec. The engine must be kept above 1,600rpm, or there is a lag before the action, but a couple of hundred rpm later it’s flying as the torque builds rapidly. Drivers will need to study the rev counter to get the most out of the engine but that is hardly a chore.

Performance figures are similar to the 2-litre petrol but apart from its occasional lack of low-speed urge, the diesel feels livelier and there is a near-20mpg fuel consumption advantage. For company car users, its C02 emissions are so low that Gordon Brown will probably have a fit of the vapours at his tax loss.

In Sport guise, handling is good; in SE form, with softer suspension, it’s a bit roly-poly but both fill their roles well. Insurance cost is said to be the lowest in its class.

The really good news is that unlike some companies, Jaguar does not charge a premium for its diesel — each version is the same price as its petrol-engine equivalent, starting at £19,995 for the basic model, although the £22,350 Sport is the one to have. All X-Types have just been given detail improvements and carbon-fibre dashboard trim instead of wood is an option worth considering.

Jaguar X-Type Diesel

Power: 2-litre turbo-charged diesel for 128 bhp

Gearbox: five-speed manual

Performance: 0-60mph in 9.5sec; top speed 125mph

Fuel consumption: average 50.3mpg; potential range 600 miles

Price: £19,995-£22,995