Do you mean you have just chosen to cease trading as self employed and you have some spare stock. Or are you referring to a Ltd company that is being officially wound up due to outstanding debts. The phrase gone under generally implies that a business has creditors who are still owed money. I would seek legal advice before you attempt to sell anything. As has been said the items may no longer technically be yours to sell. Assuming you do have legal right to sell the items then you can sell them wherever you want; Car boot, Market stall, E-bay, Garage sale, On-line sites such as this etc.
Which probably means insurance wouldn't be valid.
