LONDON—Britain’s former prime minister David Cameron said he accepted that communications with government needed to be done through formal channels after the row about his lobbying activities for financier Lex Greensill deepened on Sunday. Cameron, who was prime minister from 2010 to 2016, appointed the Australian banker as an adviser when he was in Downing Street. After leaving office, Cameron in turn became an adviser to Greensill’s now-insolvent finance firm. The Financial Times and Sunday Times newspapers have reported that Cameron contacted ministers directly to lobby on behalf of Greensill Capital, including sending texts to finance minister Rishi Sunak and arranging a private drink between Greensill and Health Secretary Matt Hancock. Britain’s Treasury has said that the former prime minister contacted Sunak and two other ministers in the department to ask if Greensill could access the government’s COVID-19 loan schemes. In his first comments on the row, Cameron said that …