Thanks a lot for your response mike, much appreciated! You're absolutely right, I was reading this article (www[dot]dieselnet[dot]com/tech/dpf_ash.php) that explains how ash is building up in the DPF, and in the 75k miles you mention, about 70% of the DPF is ash already, so many more regens will be needed more often, whilst other things will start having problems due to it as you mentioned.
Thanks for both links. The first is for an older model, as I have the R56 (63 plates), so it's the facelift version with the BMW engine. Regardless, a DPF from ebay costs about 125£, but it's the labour that will cost much anyway (if I keep my car past the 75k-80k miles mark). I have the 1.6 cooper D, so I suppose that I don't have any turbo (I thought only the SD was turbocharged, right?) ?
As far as the cataclean is concerned, thanks a lot! I found from Halfords (www[dot]halfords[dot]com/motoring/engine-oils-fluids/fuel-oil-additives/cataclean-diesel-500ml), so I'll go there today to pick it up; it's just 15 quid, so not so bad.
The directions in the ebay link say:
"Empty entire contents of bottle of Cataclean Diesel into fuel tank. Then drive for at least 15 minutes and refuel when necessary. Recommended ratio of one 500ml bottle of Cataclean Diesel to approximately 15 litres of fuel."
So, I suppose I'll use two bottles, as my tank is about 35 litres of fuel filled already. When it says drive for at least 15 minutes, does it mean (I suppose) on the motorway? or even 30 mph unstopped city driving?
Last but not least, when you say "driving the car at 3000 revs for more than 20 miles on a motorway once a week is good to keep clear", should it be continuously, or can I break this down into 10 miles each way? So that I can plan my route accordingly, 'cause 20 miles could roughly take me from Portsmouth to Southampton