The money in accounts at the Bank of England is created when the BoE buys assets and it is destroyed when they sell the assets again - traditionally, those asse

The money in accounts at the Bank of England is created when the BoE buys assets and it is destroyed when they sell the assets again - traditionally, those assets are mostly bonds issued by the treasury (or repurchase agreements or other derived stuff). The BoE does those buys/sells with an eye to ensuring that the inter-bank short term interest rate hits their target interest rate set by policy. The whole connection is pretty well explained by the modern monetary theory school of economics.