Bob Minchin wrote:

when service intervals started
increasing for petrol cars in the 90's, diesels stuck at 6000/6months
meaning (at the time, whilst fuel costs were lower for diesel) , the
increased servicing costs meant that diesels were only worthwhile if the
extended engine life was brought into the sums.
The diesel manufacturers responded and extended to 12k/12m which is the
case for my 54 plate ford diesel car.

My TDI engine is 18,000 miles/24 months, with a possible earlier oil
change depending on driving style.