Graham Smith is an unlikely heir to Oliver Cromwell. He used to work in I.T. support. He plays badminton. He lives in Reading, a commuter town 25 minutes from London. For the past two decades, however, the 51-year-old has also been the chief executive of Republic, arguably the most influential anti-royal group in the land—although, in a country still broadly fond of its monarchy, some would argue that is not saying much. The job mostly involves researching the royals’ finances, with the occasional protest thrown in.

Republic has no headquarters, so I meet Smith outside the Green Park tube station, a five-minute walk from Buckingham Palace. He is dressed in jeans, a blue T-shirt, and a nondescript jacket: the uniform of someone who does not wish to be recognized. A folded placard under his arm hints at plans for later.