Securities: debts: general points: payments under guarantee
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
Lenders commonly require guarantees over money they are lending. For example, a bank may agree to make a loan to a company, B Ltd, provided that the debt is guaranteed by C Ltd. If B Ltd is unable to repay the debt, the bank may ask C Ltd to pay instead. If C Ltd pays the bank under the guarantee it will, under general law, take over the bank’s rights to B Ltd’s debt.