The radical new Jaguar XJ will be revealed in London this July ahead of its launch later this year, and Jaguar wants to reclaim some of its traditional executive customers with the car.

Once the natural and patriotic choice for board directors everywhere in corporate Britain, the XJ has been replaced as the vehicle of choice by the Mercedes S-class. But with fresh styling, lightweight alloy construction, and new engines, the new XJ is designed to open up a new customer base.

Project X351, as the car is called, started as a reskin of the current XJ. But as the programme has developed, the engineering changes have become more extensive.

In fact, X351 will be the first Jaguar flagship to be launched with a retooled body and new engines. Traditionally Jaguar does what most other car makers do, and launches carry-over engines in a new body to keep costs down.

Much of the structure is also new; the rear structure has been changed to accommodate the XK's differential, which requires a new subframe and new mounts.

The lessons learned in the reskin and repackaging of the S-type into the XF are being applied to the XJ. For example, Jaguar started out with a coupe-like rear cabin, with a low back seat for a shallowly-raked rear window.

But the design has matured into a more practical shape, determined by the requirement to make the rear cabin as comfortable as possible for chauffeur-driven businessmen.

Styling is inspired by the XF, but well placed sources say that we should expect a much more dramatic and eye-catching look. 'People know that there’s new car coming, but they won't be prepared for anything like this,' said one source involved in the project.

The interior, too, is described as a 'big step forward'. Although features such as the XF's rotary gear selector are carried over, and the basic theme involves plenty of glossy wood and metallic trim, the new XJ takes the design to new levels of craftsmanship and quality. 'We knew we had to work on this,' said another project insider.

The flagship of the range will be the XJR, powered by the new 503bhp direct-injection 5.0-litre V8. With that amount of shove to launch a sub-1700kg saloon, the XJR is taking a major step into Bentley and AMG territory, while retaining Jaguar’s legendary balance of ride and handling.

The most critical engine is the new twin-turbo 3.0-litre V6 diesel, with 271bhp on tap. Fuel economy ought to be close to the XF's; estimates put it at around 40mpg. The car will also get the lower-powered version of the same oil-burner, with 237bhp.

The V6's peak power and torque figures are very close to the V8 TDI which appears in the Range Rover. Jaguar is therefore not likely to engineer the XJ to take the V8 unit.

Julian Rendell