Where a council claim to recover any expenses under this Act from a person as being the owner of the premises in respect of which the expenses were incurred and that person proves that he—
is receiving the rent of those premises merely as agent or trustee for some other person; and
has not, and since the date of the service on him of a demand for payment has not had, in his hands on behalf of that other person sufficient money to discharge the whole demand of the authority,
his liability shall be limited to the total amount of the money which he has or has had in his hands as aforesaid, but a council who are, or would be, debarred by the foregoing provisions from recovering the whole of any such expenses from an agent or trustee may recover the whole or any unpaid balance thereof from the person on whose behalf the agent or trustee receives the rent.