By Bansari Mayur Kamdar and Shashwat Chauhan (Reuters) -Britain’s main equity indexes closed higher on Monday as Rishi Sunak looked set to become the next prime minister after other candidates quit the race, offering investors some relief after a tumultuous few weeks in British politics. The blue-chip FTSE 100 gained 0.6%, while the domestically focused FTSE 250 index jumped 0.8%. The British pound rose in volatile trading, while gilts jumped after Sunak won the race on Monday to lead the Conservative Party, tasked with steering a deeply divided country through an economic downturn that is poi…