(Bloomberg) -- The UK bond market tumbled, driving long-term bond yields back to the highest in nearly three decades, as speculation over Prime Minister Keir Starmer future as prime minister renewed concern about the weakened state of Britain's finances. The chief concern is that any new Labour leader would be more left-leaning and may loosen the fiscal rules that have restrained borrowing. With the economy already facing a crunch from higher energy prices and faster inflation, the fragmentation of British ...