When my wife's 12-year-old BMW needed replacing she was delighted to acquire an 18-month-old Jaguar X-Type diesel. The car joined my own 9-year-old petrol X-Type, which is still going strong after 120,000 miles. The new car had a myriad of small but useful improvements but, being a diesel, the 47mpg against 30 for the petrol and lower road tax made it a dead cert. That is until I read your Q&A column mentioning something I had never heard of - the dreaded particulate filter.

I am at a loss to understand how accumulated gunge can somehow end up requiring a dual mass flywheel (whatever that is) and some other expensive parts. Would you tell us a little more please? Do some cars not have particulate filters? Are small diesel engines worse or better than large ones? If one drives the car out of the garage to retrieve the lawnmower and then back in again is that disastrous? Would a 100-mile round trip on the motorway burn off the filtered particles from earlier short drives or not?