After Stephen argues that his father has not broken the law, Lady Britomart responds by telling him that he is always doing this, and he broke the law when he was born as his parents were not married. She says this is why she and her husband separated and expands on this by explaining that Undershaft was not content with being a foundling, he wanted to disinherit Stephen for a foundling too.
Stephen stammers at this news and says this is frightful. She is not pleased either and regards him as being ‘childish’ in his embarrassment. She tells him that people of their class (not the middle classes) should let nothing disturb their self-possession. He asks her to explain further about, ‘this horrible business of my father wanting to set me aside for another son’. She reprimands him for interrupting her and tells him how the Undershaft family has had a tradition of adopting a foundling since James I. Since then, the adopted one has adopted another foundling to take over the family business: ‘Ever since that, the cannon business has always been left to an adopted foundling named Andrew Undershaft’. Stephen’s father came into the business this way and wanted to carry the tradition on, but she disagreed: ‘There may have been some reason for it when the Undershafts could only marry women in their own class, whose sons were not fit to govern great estates. But there could be no excuse for passing over my son.’
Lady Britomart and her husband also separated because she believes he has ‘a sort of religion of wrongness’ and preached immorality ‘while he practised morality’. Stephen is bewildered that people can differ over right and wrong and does not want money from his father, but she explains that is where their present income comes from. They both agree they do not want any more money for themselves. She insists that she will put her pride aside, though, and ask for more on behalf of Sarah and Barbara and he reluctantly agrees. When he finally comes round to this idea, she thanks him and also informs him his father is coming this evening and is due at 9 pm (in 10 minutes time).
She asks Stephen to ring the bell and when the butler appears she tells him to bring Sarah, Barbara and their fiancés from the drawing room. Before they arrive, she lets Stephen know she is unsure how Barbara will take the news as ‘she has developed a propensity to have her own way’ since becoming a major in the Salvation Army. She sees this as unladylike and does not know where she picked the habit up.
In this section, Lady Britomart reveals a form of class snobbery of magnificent proportions when she instructs Stephen not to be middle class in his reaction to the news about his father. Irony is heaped on irony through this character’s voice as she goes on to wonder where Barbara developed the propensity to have her own way.
This part of Act I is also used to explain the background to the Undershaft business and how it has been passed down through the generations. Lady Britomart’s class divisiveness is exposed again when she argues her son is of a class fit to govern such a concern whereas sons from lower classes should have been overlooked. Her hypocrisy is evident at this point as she has previously been critical of the trade in arms, and yet believes her son should run it. Her revelation that her estranged husband preaches immorality while he practices morality further highlights her lack of insight.