How is money destroyed when banks issue debt? Bank of England (2014):

Money can also be destroyed through the issuance of long-term debt and equity instruments by banks.

How is money destroyed when banks issue debt?
Say Bank X issues a £100 10-year bond that Person Y buys with £100 cash. Then

X has assets +£100 (cash) and liabilities +£100 (10-year bond); and
Y has assets +£100 (10-year bond) and assets -£100 (cash).

How is any money destroyed?
Generally, people do not pay for bonds with currency (e.g. pound notes). They pay with bank deposits. This means that Y has lost a deposit.

If the deposit was with X, the deposit is just destroyed; X does not hold deposits against itself.
If the deposit was with another bank Z, bank Z loses the deposit, and it has to transfer the 100 pounds to X via the payments system. X will not hold a deposit at Z.

In either case, bank deposits are destroyed, and they are a component of the money supply.