William Manchester in The Last Lion trilogy (3 books that cover the entirety of Winston’s life in great detail, clocking in close to 3,000 pages) actually goes into Churchill’s drinking habits quite a bit. I’m completely unable to cite where he said it as I listened to the audio book a few months ago now. Anyways the reports of Churchills drinking tended to be overblown and exaggerated often times by the man himself. He liked the impression it gave and thought that his alleged heavy boozing made him seem more masculine. The truth was although he certainly liked the drink he wasn’t nearly as much of a lush as history remembers him as. One line I do remember in prricular was that he did start off in the morning with a Dewars and soda but that one drink would often get him to at least lunch. Also remember that casual drinking was a much more socially acceptable thing at the time. A drink or two during the day certainly wouldn’t have been some radical faux paux and at that consumption rate would have had a negligible if any effect on his cognitive abilities. So what his actual contemporaries thought of his real or alleged consumption I am not sure but he almost certainly was not regularly drinking the heavy amounts we picture him now.