Surely if a car without a dpf still blows below the emmision standars then it complies?
Sadly I think you are missing the point. We are not talking about arguing what is or is not reasonable with individual MOT stations here.
A clear, black and white instruction has gone out - if a car was manufactured with a DPF, it must still have that DPF or it will fail.
The only "grey" area left I can see is for bored-out DPF's, which will probably pass as the MOT is largely a visual inspection (e.g. my last MOT said rear seat belt not tested as baby seat was obstructing it. It takes me 10 seconds to remove the baby seat, so basically they won't move anything to complete the MOT).
My DPF was removed so they wouldn't need to move anything to see its gone. Hence I sold my beloved Alfa 159 2 days ago, as its 8 years old and not worth the hassle. I spelt out the situation to the buyer in the ad and when he viewed it, and the price was knocked down accordingly. He was happy to take the risk and will probably have many happy years driving it.
Sadly as Alfa no longer make 159 class cars, I've had to buy a VW. Lovely car, but not an Alfa. I won't be modifying it though, I'll just accept it is not an Alfa.