My paternal grandmother (born in London to Scottish parents) used to drink her coffee and tea from a saucer because it was too hot to drink from the cup. She would pour the tea from the pot into the cup and then from the cup to the saucer. Her friend used to put a sugar cube between her teeth and suck her coffee through it. I have not seen anyone doing this since I was a little girl.
Maybe bone china cups with delicate handles transfer heat more than the mugs we use today? So the tea, the cup and the handle were too hot? If so I wonder why they did not just pour the tea straight from the pot into the saucer to save washing up. Or maybe that was considered bad manners…