Now that you mentioned it, yea the BS1363 sockets that I see ARE blackened on most of them.... I guess that makes sense; people wouldn't run a hair dryer out of a regular socket for 24 hours...
In my case, since my daily mileage is low, though I am using a cable with 16A capacity, I just limit the charging current below 10A. I park in my office during daytime for 8 hours or more. The day time charging has already been sufficient for me.