I'm not sure about that, but surely the fourth and the fifth have been known from the time of Pythagoras (300 AD or BC, I forget which) and perhaps before. I found a website once which said the fifth was known to the ancient Egyptians. Could be, because to get the fifth, all you have to do is take a string and make it half as long.

I tried to watch the BBC show but was denied because I'm not in the UK.