My X-Type has seemed to have lost its "Oomph"

[Bri-x-type]

I've had my 04 X-Type 2.0 Deisel for roughly 2 weeks and it's been a fantastic machine... Till Friday. Whenever I drove the car it felt very special, it had that kick, that "push back in the seat" edge. I love it. However I am not happy at this time. Friday evening, I was going to see my son, so I was preceding to overtake a slow moving car, Ironically an older gentleman in a 3.0 Petrol X-Type. I have never needed to drop a gear to overtake at all, always got me to 60 and beyond in a split second. Impresses me every time. But this time, I lost power, I managed to pass the other car, but not with ease, with great difficulty. White smoke began to pour out of my exhaust, the trail was probably visible from space... And every time I tried to hit my foot hard to the floor, it made black smoke pour from my exhaust. With a severe loss in performance. The car is supposed to have 130bhp... I estimated it was maybe running on 50bhp. I have had the RAC out today and the guy was great, had a look and checked the computer as I had no warning lights. And he said all live feeds were fine. He checked the turbo and had a look at other components and said they were in good condition and not to worry about that. So he Thaught it must of been the EGR... Or ERG... I'm not a mechanic so I forget. He has put a block in it and it is running a lot better and the smoke black and white has cleared. However it still has no power. No oomph. Feels like it's running on a 1.0 Corsa engine.. So can Any one help me? I want my car back to normal! Cheers.

[Bri-x-type]

Just to add, I don't drive th car in an erratic manor, so I know it's not because of working it too hard.

[KEN33Y]

I would have said start with the Turbo however, the RAC choppy have covered that. I would now move on to the EGR, there are plenty on here who have encountered problems with the EGR and should be able to share advice. Try doing a search for entering the letters erg

[Bri-x-type]

I've got quite a few plans to try now, I'm amazed at the help I've received. So thanks very much