Whatever you may think (or not) about the effect that noise pollution has on the environment and the rest of society, the legal noise level in the EU, UK included, is 82 decibels, +/- zero (excuse the pun). Notwithstanding that, if the noise levels created as a result of modification or whatever, exceeds that of the original at type approval, then that's not allowed under law either.
Since the vehicle is technically not road-legal then, it probably renders your insurance invalid too.
Do you really want to go that road?
.... discuss (but quietly please !).
David