To most MOT testers, they would interpret your car with an unsilenced centre section and a Spoon N1 as to not meet the requirements of the test, rendering it "non-roadworthy". Whether the MOT tester would actually fail your car for this depends on the tester. You could leave it down to chance, you could ask ahead of time, you might need to grease the wheels, so to speak.
When I get my car MOT'd, I just put the original backbox in the boot, and they put "Original exhaust fitted at time of test", as the garage is directly opposite a police station, and the tester wanted me to have the original in the boot so that the garage could not be brought into disrepute for deliberately passing a car that should obviously fail on noise emissions, in the event of me getting pulled over as I left the garage.