This phrase implies that something is simple and an easy way of making money. It dates back to medieval England when criminals could be sentenced to death by hanging – in fact this practice only ended in 1964. By tradition the hangman was allowed to keep the rope after the execution.
Such was the sensation surrounding many high profile or ‘celebrity’ hangings – where large crowds often gathered to witness the executions (one hanging – of the murderers Haggerty and Holloway in 1807 drew a crowd of 40,000 people) that the hangman would cut the used rope into small lengths and sell it to members of the crowd.
The most notorious of these hangmen was William Calcraft, from Little Baddow, near Chelmsford in Essex. He was chief hangman from 1829 to 1874; the most active and longest serving executioner in British history. It’s believed that Calcraft conducted 450 executions in his lifetime (including 34 women), of which at least 388 were public.
A useful source of extra income hence – Money for Old Rope.