Tata Motors' luxury car unit Jaguar has been explaining why it is upgrading the 2.2-litre diesel engine in the XF after only a year, a move which could potentially annoy some existing owners.

The 2.2-litre diesel was introduced for the 2012 model year with an output of 190hp and CO2 emissions of just under 150g/km. These figures made the first four-cylinder XF - it uses an engine from the Ford-PSA diesel joint venture - competitive and attractive in the majority of western European markets.

But, within weeks of the car going on sale, some governments, led by Holland and Belgium, changed their emissions-based car taxation structures. The suspicion is that they wanted to raise more tax revenue and were cloaking it in environmentalism.

The immediate impact on Jaguar was that, overnight, the XF2.2D became around EUR6,000 more expensive in the Benelux region.

Jaguar responded by bringing out a less powerful, 163hp version of the engine. But that still left the original unit largely unwanted in several countries.

The upgraded engine not only delivers an extra 10 horsepower - now up to 200 - but, crucially, brings emissions down to 135g/km so that it will neatly side-step the Dutch and Belgian tax changes.

Here in the UK it means lower taxes, especially for business drivers, plus better fuel consumption and performance.

Two-thirds of the improvements are down to work on the engine and transmission electronic control units with the rest coming from changes to other components, mainly the tyres.

The new engine will in the XF saloon and new XF Sportbrake estate car [wagon] this month. The Sportbrake is Jaguar's first large estate car, initially only for Europe and offered solely with diesel engines.

Jaguar is particularly proud of the fact that, despite the car having a vast load area and a wide tailgate opening, its body is 5% stiffer than the saloon's.

This has been achieved with the help of a steel collar running all around the tailgate opening, reinforcements beneath the floor and in the structures above the doors, and a bracing 'fez' on each rear suspension turret - so-called  because of its resemblance to the late comedian Tommy Cooper's famous headgear.