Bank accounts are an obvious and fruitful avenue of enforcement for judgment creditors, and with good cause -they are a readily available pot of money held by a reputable institution that is likely to comply with any court order given to them.
Banks holding money for a judgment debtor are the target of domestic enforcement action in the form of third party debt orders. These orders carry with them an administrative burden for the bank. While it can deduct a statutory sum of currently £55 from the debt to cover its expenses this nominal amount (if deducted at all) may not reflect the actual compliance cost to the bank.
