In primary school, our SPMG maths books talked about "New Pence". I, logically, concluded that new pence were the plastic ones used in maths lessons (they had 'new pence' written on them, after all), while old pence were the metal ones you pay for things with in shops.
My parents used Fahrenheit for body temperature well into the 1990s. I expect they were reasonably bilingual in a professional setting, and just defaulted to whatever the thermometer they were using was calibrated in (at home we had a Ye Olde mercury one, until it broke (which was worth it for the blobs of mercury) and was replaced with a newfangled alcohol one).