Let's suppose someone is house-sitting for an associate, and they are away on holiday. Then some enforcement agents come to settle a debt, claiming to be entitled to seize any possessions at the address. What if the majority of the possessions in the property at the time of the enforcement visit belong not to the debtor, but to the house-sitter? What is the situation here then, legally speaking?
The house sitter has to prove ownership
The law, at para 10, Schedule 12 of the Tribunals, Courts and Enforcement Act 2007 is that:
An enforcement agent may take control of goods only if they are goods of the debtor.
Bailiffs can consider at first sight “prima facie” any goods are the property of the debtor and the burden of proof who owns seized goods lies with the debtor or the owner [in this case the house sitter]: Observer Ltd v Gordon  - but does not apply to vehicles [they should check with DVLA] Source
This means they can sieze goods they believe are owned solely by the debtor or jointly with a co-owner but not "third party goods" that belong to someone else - therefore onus is on the the house sitter to prove their ownership. If this cannot be proved to the bailiffs' satisfaction and they take some "third party goods" then the house sitter may lodge an interpleader claim as per Civil Procedure Rule 85.4 to recover their goods.