Why does my garage consumer unit buzz when the kettle is on?
Buzzing is a clue that there is a bad connection. This could be a bad breaker contact. On this side of the pond I have had top name brand breakers do this. My solution at least short term is turn that breaker on and off 10+ times with nothing plugged in. This seats the hammers in the breaker displacing the crud that was causing the problem. If the buzzing quits that solved the problem for now. I say solved the problem for now because if the arcing was severe it may return when this circuit is heavily loaded and then it's time to replace the breaker. It could be a loose wire lug also but I have found the breaker to be the cause most often even in large 3 phase systems the on off seats the hammers and things may be normal.