Act 1 opens on a dismal Sunday afternoon in Jimmy and Alison's cramped attic in the English Midlands. Jimmy and Cliff are attempting to read the Sunday papers, plus the radical weekly, "price ninepence, obtainable at any bookstall" as Jimmy snaps, claiming it from Cliff. This is a reference to the New Statesman, and in the context of the period would have instantly signalled the pair's political preference to the audience. Alison is attempting to do the week's ironing and is only half listening as Jimmy and Cliff engage in the expository dialogue.
We learn that there's a huge social gulf between Jimmy and Alison. Her family is upper-middle class military, perhaps verging on upper, while Jimmy is decidedly working-class. He had to campaign hard against her family's disapproval to win her. "Alison's mummy and I took one look at each other, and from then on the age of chivalry was dead", is one of the play's linguistic gems. We also learn that the sole family income is derived from a sweet stall in the local market — an enterprise that is surely well beneath Jimmy's education, let alone Alison's "station in life".
As Act 1 progresses, Jimmy becomes more and more vituperative, transferring his contempt for Alison's family onto her personally, calling her "pusillanimous" and generally belittling her to Cliff. It's possible to play this scene as though Jimmy thinks it's all a joke, but most actors opt for playing it as though he really is excoriating her. The tirade ends with some physical horseplay, resulting in the ironing board overturning and Alison's arm getting a burn. Jimmy exits to play his trumpet off stage.
Alison and Cliff play a tender scene, during which she confides that she's accidentally pregnant and can't quite bring herself to tell Jimmy. Cliff urges her to tell him. When Jimmy returns, Alison announces that her actress friend Helena Charles is coming to stay, and it's entirely obvious that Jimmy despises Helena even more than Alison. He flies into a total rage, and conflict is inevitable.