Our office closes on the 19th too and will reopen on the 2nd with only me in attendance. The remaining staff will be returning the following Tuesday. I have informed the council that this is the intention and as the staff are taking annual leave, I cannot see why the council should be getting involved. I don't ask them to approve the arrangement as I am the line manager for my staff.
Major assumption on your part that it is a freebie - council staff are entitled to their holidays and are probably using their holiday entitlement, as would anyone.