AS a motoring journalist of some years experience I probably shouldn't admit to this, but I have been thoroughly duped by our long-term Mazda6 test car.

It was during a particularly busy time both at Fleet News and at home that I picked up the keys to the car and, having not taken too much notice of what I was driving, I mistakenly thought for the first day that this car had a petrol engine under its bonnet.

It wasn't until I stopped for fuel and opened the filler flap that I saw the word 'diesel' stamped on its underside.

Now you can take this piece of information two ways – either I am complete fool who does not deserve to be called a road tester or this 2.0-litre diesel powerplant is a very smooth one indeed.

I would, of course, contend that the latter is the case. In my book, this car has one of the quietest and smoothest diesel engines I have ever driven – no wonder the Mazda6 won the best upper-medium car award at this year's Fleet News awards.

The other reason I mistakenly assumed this engine was a petrol variant is because it behaves very similarly to a petrol engine. With 134bhp on offer, 0-60mph comes in a respectable 10.6 seconds and the car will achieve a top speed of 123mph. But with 229lb-ft of torque available at 2,000rpm, there is plenty of low-down grunt, so perhaps this was the clue that should have given away that this is not a petrol model. Add to this one of the best-handling chassis in the upper-medium sector and you have a car that drives like a dream on the road.

On the downside, the general ambience of the cabin doesn't really match up to the last test vehicle I had, the Honda Accord in Executive trim. This car has leather seats as standard (although no satnav) and exudes an upmarket air of quiet affluence, while some of the Mazda's plastics seem comparatively cheap and tacky. But then again the Honda doesn't handle as well as the Mazda so it is rather a case of swings and roundabouts.

Some of the rival manufacturers are now launching Euro IV compliant diesel engines, which means the driver doesn't have to pay the 3% benefit-in-kind tax diesel supplement that the Government imposed on 'old' style engines. Therefore, a 40% taxpayer will have to cough up £135 a month for the benefit of driving this car, as opposed to £116 a month if it had complied to Euro IV emissions standards.

Taking over the keys to the Mazda could not have come at a better time. My 22-year-old son, who has been living with me for the past three years, has just moved into his own house (hooray!) and was expecting me to help shift all his goods and chattels into the new abode.

You'd be amazed at how much you can cram into an estate car with the seats folded down.

So far I have managed a double bed, chest of drawers, fridge, washing machine and cooker (although obviously not all at once!). It has taken a few trips but was well worth it for the peace and quiet I will now be able to enjoy in the company of my cat, Crumble.

Company car tax bill 2003/04 (40% tax-payer): £135 per month