The First Prime Minister? More recent than you might think ...

Britain’s unwritten constitution did not recognise the position of Prime Minister until relatively recently. All the so-called prime ministers from Walpole to Balfour were First Lords of the Treasury. The position of Prime Minister was finally acknowledged on 5 December 1905 when Henry Campbell-Bannerman was appointed to the post.

The need to make this change had been anticipated by Edward VII earlier in the year when he realized that Campbell-Bannerman, as a mere commoner, ranked lower than some other members of his Cabinet. He ordered the drawing up of a warrant to declare that the Prime Minister was the fourth ranking person in the Kingdom, behind the two Archbishops and the Lord Chancellor.

You can find more anecdotes in my 500 Echoes:

https://www.amazon.co.uk/gp/product/B0B7DZ6YXH/ref=dbs_a_def_rwt_hsch_vapi_tkin_p2_i2