Just for information:
Filter forcing regulations came into effect January 2013 for all diesel cars (Euro 5b level), where over the New European Drive Cycle (NEDC) particulate number (PN) is measured, the required level being less than 6x10^11 #/km.
What works in everyone’s favour is that PN is hard (read impossible) to measure at your local MOT centre, so you've only got to worry about the PM (particulate mass) + CO + HC + NOx (the normal pollutants that they can measure). Even when gasoline vehicle legislation becomes filter forcing (Sept 2014) it’s unlikely PN could be measured at an MOT centre, so I think you’re all safe for a long time.
It seems from the previous posts that the MOT test can still be passed without a DPF. I would imagine that the DOC (diesel oxidation catalyst) in the system is taking out enough CO and HC that the relatively easy MOT test can be passed – it may however be taking you closer to the limit. My company doesn’t make these catalysts, I believe they’re made by BASF, so I can’t comment on the metal loadings on the DOC – but they appear to be sufficient to pass.
As a previous poster said, the filter is on there for good environmental reasons – the smallest particles that come out are one tenth of a micron in size and are likely carcinogenic, but I do agree, the filter comes at a high price in terms of car performance.
Oh, as an aside, some people were also posting about using high pressure water to remove the soot and ash from the filter. It would be much better, if possible, to use compressed air (blowing from the outlet side). The water may partially dissolve the catalyst, washing out the Pt and Pd from the filter – making it less effective.