Rattling baffler

[Mattastic]

My GS125 has developed a real rattle from the exhaust, which one of my neighbors reckons is the baffler in the exhaust that has become loose. He also says that there is very little I can do about it as the exhaust is sealed and I won't be able to gain access to it. It only becomes apparent between 2k-4.5k revs but it is obviously going to get worse if it is loose.

1.) Any tips on what I could do?
2.) Would this be enough to fail it's MOT that is due in a couple of months?
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Too skint to buy a bike