(I'm no electrician but) switches on 13A sockets do fail. shortly after buying my current house one night I turned off the TV checked kitchen, back through sitting room and TV LED was still on. Socket switch was off. Unplugging obviously worked. The switch had failed but failed in the "ON" setting.
I then decided to change every socket in the house from the cheapo unbranded ones to quality MK ones. I felt it important that when you switch something off it really should go off.