FORD'S Achille's Heel has always been its old school diesel offering. While Volkswagen and Peugeot have pioneered common rail turbodiesel engines, Ford has stuck with old fashioned and unrefined oil burners.

But the Focus is still the UK's best-selling car and the best-selling diesel car, despite only being available with a slightly agricultural diesel engine.

So what hope do the other volume manufacturers have now that Ford has finally launched common rail engines to its lower-medium challenger and also into its larger Mondeo stablemate?

The answer appears to be not much, because the new family of TDCi engines are superb - a million miles away from the coarse TDdi units that have been in service.

Designed and built at Ford's Dunton diesel technical centre, the new Duratorq TDCi units are on sale now in 1.8-litre guise for the Focus and 2.0-litre capacity for the Mondeo. They will be marketed as a premium addition to the range and will be sold alongside the existing TDdi units.

However, TDCi will not be available in all trim levels on the Focus, although it covers the entire Mondeo range.

This move extends Ford's diesel offering in the traditional heartland of the fleet market. And the fleet market seems to have been Ford's focus (an unintentional pun) as it prepares to ride the wave of increased oil-burner sales.

Ford admitted at the launch of the TDCi engines at the Goodwood circuit in Sussex that it had been behind the market leaders when it came to diesel - most notably Peugeot and Volkswagen with, respectively, their HDi and pumpe duse technology.

And with diesel sales set to rocket as the emissions-based benefit-in-kind tax system is introduced in April, Ford knew it had to act.

And Ford certainly has. As well as offering what is now the pick of the diesel engines, Ford has also added equipment to both the Focus and Mondeo for the 2002 model year line-up and has also managed to keep prices competitive.

The entry-level Focus TDCi in five-door Zetec trim costs £14,345 on-the-road - a £1,000 premium over the TDdi model, and slightly more than the £14,200 Volkswagen Golf TDI PD 100 S - although the Focus offers 115bhp as opposed to the Golf's 100bhp.

In addition, Ford has increased specification on the Focus, with Ghia models now offering global closing power windows, new style alloy wheels, body-colour door handles, new interior trim and footwell lighting as standard.

LX models have interior trim tweeks, Quickclear heated windscreen and new wheel covers. Zetec versions now receive a leather steering wheel and sports suspension.

In the Mondeo, entry to TDCi comes in at £16,145 for an LX saloon - undercutting a Volkswagen Passat TDI PD 130 S by £340.

In the Mondeo, Ford has added £500 of extra equipment while increasing prices by £50. New features include standard-fit emergency brake assist, a key safety feature designed to reduce stopping distances.

Also new is an automatic rear windscreen wiper which is activated when reverse is selected. These specification improvements make the Focus and Mondeo even harder to beat. Volkswagen should be worried and Vauxhall will have to ensure the new Vectra is a very good car indeed.

The TDCi engine in the Focus and Mondeo is excellent and the gearbox used with this engine is far better than before.

The first thing you notice about the TDCi engine is how quiet it is - at idle its rattle and noise are suppressed so well that it must rank as one of the quietest diesels on the market - a world away from the tractor-like rattle of the TDdi unit.

The moment you engage first gear and set off you notice the difference as well. The engine makes smooth progress through the revs and seems quite happy to carry on to the red line. With so much torque on offer you can make swift progress no matter what gear you are in.

In the Focus in particular, the performance is quite eye-opening, with the front wheels struggling to transmit all the power under heavy acceleration in a low gear.

Before you know it you are travelling well above the speed limit in both the Focus and Mondeo, although wind noise in the Focus makes you appreciate your speed more. In the Mondeo, noise is well contained, meaning you don't always appreciate how fast you are travelling.

While neither car offers improvements in CO2 emissions and fuel economy over the existing TDdi units, they are far more rewarding, and easy, to drive.

However, both models fall into the lowest diesel tax band (18 per cent including the 3 per cent diesel supplement) for drivers from April, so they can appreciate the double boost of low tax bills and a genuinely rewarding drive.

Ford's chassis know-how is well known on the Focus and Mondeo and the new common rail diesels take the Mondeo and Focus up another notch. The opposition should be very worried.