U.K. electricity for delivery a day ahead gained, boosting profit for operators of plants that burn natural gas, the fuel for about 40 percent of Britain’s power generation. Baseload electricity for next-day delivery rose as much as 4.2 percent to 28.65 pounds a megawatt-hour, according to prices on Bloomberg from the energy broker Spectron Group Plc. It traded at 28 pounds a megawatt hour at 8:52 a.m. in London. Baseload power is delivered around the clock.