Got the DB killers? They do make a difference but even then I would be modify them with whatever I could to pass the test i.e stuff in tightly rolled chicken wire etc. if you' ve got the slip ons wire the flapper closed as well.
The chap who does my mot on my 1299 with Akras with no bd killer told me it’s really up to the individual centre what is classed as excessive noise. He was more bothered about having the correct sized number plate. Most bike garages near me will pass a bike with Akras.
As others have said it's down to the garage, find a different one i would.
I remember i used to take my bike to Demon Tweeks for MOT as it was soooo cheap but they would always insist on having db-killers in, which i always forgot. Funnily enough they sold them there.
Thanks for the replies, I will try another MOT centre. I have been pointed to a south London “deaf” MOT inspector, he also likes his palms greased with a crisp £20 and anything passes. going to give him a try.