Episode 4 Covers the Great Smog of 1952.
In December 1952 the country is in the grip of a deadly smog, which causes thousands of deaths, including that of Churchill's secretary Venetia Scott. Elizabeth confronts Churchill with the fact that the smog has been caused by chimney smoke from Conservative-built power stations, and his detractors seize upon this, calling for his resignation.
However he rises to the occasion with hospital visits and the promise of a public enquiry, leading to the Clean Air Act, and Elizabeth decides against his dismissal. Afterwards Queen Mary tells her that it is not in the monarch's remit to engage in politics.