Report on BBC Watchdog last night:

Is your diesel filter out of kilter?
The part in question is called a Diesel Particulate Filter or DPF. It's fitted to the exhaust to trap the soot and reduce emissions. The part was introduced to bring cars in line with new EU green emissions rules. But if you use your car solely for city driving then you could be in trouble.

The part usually cleans itself when the engine runs at high speeds - a process called regeneration. If this hasn't happened for a while, a warning light indicates that the filter is getting blocked. It must then be cleared by driving the car at high revs for a sustained period of time. This is easily done on the open road but is much more difficult to do around town.

Watchdog has received over two hundred complaints about problems concerning diesel particulate filters. And it's a problem that affects diesel cars made by most manufacturers. Some drivers have had to pay hundreds of pounds to have their filters cleared whilst one customer needed a replacement costing over £1000:

BBC - Watchdog: Is your diesel filter out of kilter? (http://www.bbc.co.uk/blogs/watchdog/2011/10/diesel_particulate_filters.html)

i know someone who has got a diesel and they use it in an urban environment,they has no problems what so ever with the dpf,her other half also uses the car on the motorway once a fortnight..

the reason they've had no trouble with it is because they don't take the car into the higher gears,only use the first 3 gears and keep the engine revs above 2k..

also comes down to the fact those who change from a petrol engine to a diesel don't really know how to drive one..