LONDON—The husband of UK charity worker Nazanin Zaghari-Ratcliffe, who has been detained for more than five years in Iran, has gone on a hunger strike again after a court decided she has to spend another year in prison. Richard Ratcliffe started his fast on Sunday outside the British government’s Foreign Office in central London. He plans to maintain a “constant vigil” by sleeping in a tent outside the building’s main entrance in an effort to pressure Prime Minister Boris Johnson to secure the release of his wife and other detained dual British–Iranian nationals, Amnesty International said. Zaghari-Ratcliffe served five years in prison after being taken into custody at Tehran’s airport in April 2016 and convicted of plotting the overthrow of Iran’s government, a charge that she, her supporters, and rights groups deny. In May, she was sentenced to an additional year in prison on charges of spreading “propaganda against the …