Looking at it from a different point of view...
The switches are burned but not the connectors nor the three individual "plug inlets".
I'd be looking for a common factor in these student houses and the one which springs to mind is cleaning. A good squirt with many cleaners will both corrode the contacts and create a track. Might be nothing wrong with the sockets.
Perhaps worth talking to the landlords - do they have a cleaner for the premises?
Either cleaner or students may be trying to de-grease the sockets and be over generous with the fluids.
Edit just read original post - "kettles" - again suggests fluid as condensate over/against socket.
The switches are burned but not the connectors nor the three individual "plug inlets".
I'd be looking for a common factor in these student houses and the one which springs to mind is cleaning. A good squirt with many cleaners will both corrode the contacts and create a track. Might be nothing wrong with the sockets.
Perhaps worth talking to the landlords - do they have a cleaner for the premises?
Either cleaner or students may be trying to de-grease the sockets and be over generous with the fluids.
Edit just read original post - "kettles" - again suggests fluid as condensate over/against socket.