Yields on U.K. government debt tumbled after the Bank of England said it would temporarily buy securities. “The purpose of these purchases will be to restore orderly market conditions. The purchases will be carried out on whatever scale is necessary to effect this outcome,” the central bank said. It also postponed planned gilt sales for next week. The yield on the 10-year gilt /zigman2/quotes/211347177/realtime BX:TMBMKGB-10Y +1.58% fell 27 basis points to 4.24%.