Are political careers facilitated by family networks? We address this question using a novel dataset assembled from various sources and combining information on the political careers of British MPs with information about the family trees of the British aristocracy. Our data span almost two centuries (1831-2023) and document the evolution over time of the background of British MPs, their social origin (in particular whether aristocratic or not), education (university and school attended), profession and political experience. Using information on family trees we measure MPs' distances from relatives with nobility titles and their centrality in the aristocratic network. We use these indicators to assess the role of aristocratic ancestry and connections in determining election and career progression. These indicators, calculated at birth, explain a large part of an early start advantage, i.e. the lower age of entry into the House of Commons. Progression into the Cabinet is also facilitated by aristocratic connections, both directly and indirectly, via longer experience (in years) accumulated in parliament due to the early start advantage. This career advantage is smaller for access to the Cabinet than for entry into the House of Commons. We also show how the decline of the aristocracy in British politics is mostly due to its decline as a source of political personnel for the Conservative party.