Thanks. I have received this as a reply
Your legal advice is incorrect. A lien also arises at common law so Dentsu Aegis Network is entitled to retain possession of your property until the debt is settled.
We should be grateful if you would confirm when this will happen so that we can resolve this dispute amicably and without the need for further action for recovery on our part."
Is this correct and if so is there anything I can do about it? I'm guessing there a precedents for this type of thing.
It may be worth noting that this is a large, multinational corporate.