Fact I didn’t know: the 4th Doctor’s scarf is so doggone long because of a misunderstanding. Costume designer James Acheson dropped off a supply of various yarns to knitter Begonia Pope, asking her to knit a scarf for the new Doctor. Whatever may have been intended, what resulted was a 20-foot scarf that used all the yarn supplied.
I found this out at doctorwhoscarf.com. This site also includes patterns and information about creating your own.