Saturday’s ad is for the British beer by Inde Coope, Double Diamond Burton Pale Ale, from probably the 1950s. The ad shows a nice illustration of a tray with a bottle and two glasses, one full, with a second bottle about to be opened. But I confess I’m confused about this bit of the ad copy. “Get outside a Double Diamond and you feel more like yourself again.” Is “get outside” a British idiom for drink a beer?
Yes, it’s just a question of perspective: you can say you’re pouring the beer into you, or you can say you’re getting outside it. It’s one of those hail-stout-yeoman-of-the-bar real-ale-twat idioms.