I don't know if it's getting stricter next year, but currently I believe the mot rules say it can fail if the car is noisier than a similar car with stock exhaust.
A quick hunt on Google says this came in around 2010ish and people often get advisaries but not been able to find anyone failing with it.
Use a garage that understands performance cars.
"yes sir, this car is a sports car, a similar car car with stock exhaust you say? Well this Pagani is also a sports car, let's compare exhaust volume"