UK borrowing costs have risen sharply as investors react to growing uncertainty around Sir Keir Starmer's leadership and what it could mean for future government spending plans. Long-term gilt yields reached their highest level since the late 1990s, while 10-year yields also climbed to levels not seen since the financial crisis. This matters because higher yields increase the cost of funding government debt, reducing room for tax cuts or extra spending. The move also comes as higher oil prices raise inflation concerns, leading markets to expect the Bank of England may need to raise interest rates to keep price pressures under control. The pound weakened against both the dollar and the euro, while UK government bonds saw further selling, especially at the long end of the market.