Japan: 1981 would be my best guess. I was not able to find an image of the back cover, so it’s hard to tell if this is another early/’undercover’ UD label title.
Source: audience recording from the London Rainbow, 20 June 1980
Side A : The Ides of March / Sanctuary / Wrathchild / Prowler / Remember Tomorrow
Side B : Killers / Running Free / Another World
Side C : Transylvania / Strange World / Charlotte the Harlot / Phantom of the Opera
Side D : Iron Maiden / Drifter
Reissued at least twice on vinyl in the mid to late 1980’s, for example on the Screaming Oiseau label as a fake-Japan release Revelation Live At The Rainbow with a misleading quote on the back (“Somewhere on tour 86/87) and on Mongkok Records (probably not made in Hongkong):
Cover art simply nicked from the official 45, released in February of 1980.