I want to know the answer to the following question:
When was prime minister first mentioned in a government document in the UK?
All the background I'm provided with is that "The prime minister sits in the cabinet solely by virtue of occupying another office, either First Lord of the Treasury (office in commission), or more rarely Chancellor of the Exchequer (the last of whom was Balfour in 1905).". Is that enough to answer the question?
Answer: no