Churchill was an out spoken critic of alcohol prohibition. He spoke against it for ideological reasons, saying "No folly is as costly as the folly of intolerant idealism". These arguments are the same that many critics of cannabis prohibition use. So was Churchill also against cannabis prohibition?
The simple fact of the matter is there seems to be no record thoughts of his on the matter. The arguments made in that excerpt are specifically in relation to alcohol prohibition, and whilst one may draw parallels between that reasoning and contemporary legalisation campaigners, it would be erroneous to state that he was therefore a cannabis advocate! Neither Jenkins nor Manchester makes any note of his view on recreational drugs beyond alcohol and tobacco - both of which they were able to examine in great detail! Therefore, without straying into "what would he think if he were around today" territory I don't feel that we can offer any conjecture on his view of drug legalisation.
