How does the Winslow Boy give you a holistic understanding of the political, social, and economic climate of England? Support with references from the play and base on analyses of language, form, and structure of the play.

I think the theme of "family honor," and the lengths to which the Winslows will go to protect it, is used by Rattigan as the basis for a complex critique of British notions of justice, marriage, and the class system.
Justice: The play draws a distinction between "justice," or the finding of the Admiralty, and the notion of "let right be done," or finding the actual truth of the matter. Ultimately, what is at issue is less Ronnie's alleged crime of stealing five shillings and more the tradition and bureaucracy that mandates his expulsion from school and his eventual trial. The scene in act II where Sir Robert examines Ronnie and is convinced of his innocence is meant to be understood as a moment in which the truth comes out, but, in fact, Sir Robert's involvement only facilitates what can only be thought of as a kind of transaction: the Admiralty does give up its case, but only after the process has consumed the Winslow fortune and left their "honor" a hollow shell. (In this sense the play recalls the Chancery suit in Dickens's Bleak House.)
Class: The Winslows are representative of the rising British middle class because they are not truly wealthy, but nevertheless aspire to a higher social standing. Much of the first act is concerned with the father discussing (or criticizing) his children's prospects for the future. Although Ronnie, according to his father, is a brighter prospect than his brother, who is currently studying at Oxford and looking forward to a career in the civil service, it is Ronnie's expulsion that throws the brother's future into doubt, since the family can no longer afford his tuition. There is a kind of dissonance in the Winslow's apparent prosperity and the sacrifices they must make to pursue Ronnie's case. While on the face of it it may seem like a noble sacrifice, there is also something degrading about it.
Marriage: Ronnie's brilliant suffragette sister, Catherine, is also affected by the trail and its outcome. Catherine has entered into an engagement with an Army officer, the transactional nature of which is made plain in the first act when the father discusses the twelve hundred pounds he has set aside for her dowry. The engagement ends in act three when it becomes clear that Catherine's fiancé is more concerned about the dwindling Winslow finances than he is with Catherine herself. Catherine's intelligence and independence, best exemplified by her urging her father to pursue the case over her fiance's objections, prove to be of little value in helping her family improve their social standing. The play closes with her marriage prospects still in doubt.
It is perhaps ironic that the entire play is set in that symbol of British gentility, the Winslow's drawing room. While Ronnie's vindication may seem like a vindication of the Winslow name, the personal and financial costs of that victory are very high and serve to undercut their ability to attain a higher social status.