Britain's Prime Minister Keir Starmer in Paris on April 17. He promised on Saturday he would "listen to voters" after his Labour party received a historic drubbing in local and regional elections. | AFP-JIJI Prime Minister Keir Starmer’s political problems have likely grown too big to solve with a single speech. For now, he will try to forestall an immediate challenge to his job. Starmer will make a last-ditch effort to save his premiership on Monday with a politically charged address designed to hold back calls for a change in leadership atop Britain’s governing Labour Party. Several would-be contenders are sitting on the sidelines, weighing whether to join a scramble for the prime minister’s job as soon as the premier stops talking. The speech in the wake of Labour’s sweeping defeat in local elections on Thursday , including a historic loss of control in the Welsh parliament, is easily the most consequential event of Starmer’s political career.…