It will fail the mot having a cat bypass, as your car is charged I strongly recommend a cat bypass due increase in hydrocarbons which will damage the cat. All I tell the mot tester's: The car hasn't a cat on so I've put the cat in the passenger seat to change for the car to pass the mot. They usual say bugger that I'll get my hands dirty and stick the probe up another cars exhaust. 10 quid cash always sorts it!!