Thanks everyone for the responses!
So the latest is, that messages have been exchanged with the dealer. I mentioned that the difference in emission values from the test he had done to what I had done was a 365% increase so it was a huge difference.
I have the car booked in with an ex bmw service engineer on the 5th and he's fitted many acs springs to 335d xdrives. He knew exactly what I was talking about in regards to possibly having a remap and or dpf internals removed. He also said he can check the pressures of the dpf via diagnostics using a laptop and determine whether the dpf internals have been removed and whether the coding has been altered to stop the engine light coming on etc. So no removing of the sensor for a borescope is necessary, which is good.
Plus he could look at the car quicker than my local bmw dealer so I was pleased about that.
So I told the dealer that I'll let him know the outcome and if its bad then that will be the decider as to whether I reject the car since I'm well within my consumer rights to do so, especially if I've been sold an illegal car.
He just replied with please free to do the inspection and that he hasn't sold an illegal car.
I haven't responded to that since I'll see what happens on Wednesday.
The car is a really nice spec though but I don't know the history even though the dealer said he knows the car after selling it before.
I've informed the finance company of the fail and of the inspection on Wednesday. I said I'll keep them updated once I know the outcome. They just said thanks for letting them know and they'll do what they can to help.
I thought about recording conversations, but our exchanges have been via email today which is preferable to have them as proof.
The dealership is apex performance cars in Huddersfield. They also have a much larger site called shaks specialist cars.
Thanks,
Connor.