“Remember, remember 5th November” is an expression referring to the celebration of Guy Fawkes Day. Guy Fawkes Night takes place on November 5th each year. “Remember, remember 5th November…” is the first line of John Milton’s poem In Quintum Novembris (On the Fifth of November). The poem alluded to the happenings on November 5, 1605.
https://www.worldatlas.com/articles/what-does-remember-remember-the-5th-of-november-mean.html

