Green’s Dictionary of Slang

used as an intensifier in such combs. as bloody well, jolly well, damn well adv. etc.

1884		Sessions Papers 8 Jan. 325: If you don’t bleeding well let me go.
1894		A. Morrison Tales of Mean Streets (1983) 40: You’re a damn brute. Y’ought to be bleedin’ well booted.
1898		Kipling in Morning Post 8 Nov. 5/1: My friend, you made a mistake, and you jolly well know it.
1902		Bulletin (Sydney) 13 Dec. 20/3: He […] told me if I wanted more I could darn well pay for it, or make myself scarce.
2001		K. Sampson Outlaws (ms.) 11: He should’ve well been there.