It would be “absolute madness” for the next prime minister not to press ahead with the Sizewell C nuclear plant, Boris Johnson has warned as he confirmed £700 million of government investment in the project. In what was billed as his final speech before he leaves No 10 Downing Street next Monday, the PM told an audience at the Sizewell B nuclear plant in Suffolk that the next government should not take the “short-termist” approach that had bedevilled nuclear power policy in the past.