These gilts or bonds work exactly as you’ve described. So how do you get margin called? You mix in 5-10% high risk, high reward securities to try to make a prof

These gilts or bonds work exactly as you’ve described. So how do you get margin called? You mix in 5-10% high risk, high reward securities to try to make a profit and buy, on margin, extra gilts/bonds to try to hedge the risk. You’ve now gone from a durable bond as long as it’s held to maturity to a derivative based house of cards vulnerable to bank runs.