From a hotel group who decided to mix it up and serve you booze that's not in the form of tiny, crazily overpriced bottles from a mini-fridge, Mansion's an Earls Court cocktail bar that's smartly dressed w/ hanging bowler hats for lights and cut-glass goblets on the tables.
The extensive drinks menu is divvied into sections named for some of Britain's more notable peeps -- Norman Lockyer, who discovered helium (and therefore silly voices) gets chemistry-aided action like a Carbonated Negroni made w/ a sort of hybrid SodaStream/ cocktail shaker that's unique in the UK.
Other luminaries? A whiskey-soaked Churchill section (Bobby Burns, juleps, etc.); the absinthe-fueled Oscar Wilde (sours, gimlets…); the gin-loaded Hitchcock (brambles, aviation...); and the champagne-laden Freddie Mercury, whose Frenck 76 has vodka, and possibly some kind of magic.
They're also slinging their own home-brewed house ale, which they'll use to cook you a half pint of prawns, alongside sandwiches (steak, pulled pork, etc.), and slow-cooked pork ribs in cider, all of which should give you something to sleep on.