Regulated (rent Act or Protected) tenant voluntarily submits a move out date to Council tax billing authority, and obtains an alternative accommodation.
No notice to quit is served on Landlord and rent payments are stopped by the regulated tenant.
Tenant do not return keys and give no forwarding address. Landlord can not serve notice to terminate tenancy on the protected,(rent Act tenant).Therefore Regulated (protected) tenancy remains active.

Billing authority transfer Council tax liability over to the Landlord although the protected tenancy has not been terminated legally. First tier Tribunal make the assumption that the fixed term had ended and the current active tenancy is a protected,secure statutory periodic tenancy for a period of MORE than 6,months!. As tenant has retained material interest in the property for more than 6 months, tenant has effectively retained material interest in the appeal property and therfore, tenant should be liable for the council tax until the Regulated tenancy is legally terminated by the tenant, especially as Landlord has no legal grounds to terminate this special type of protected tenancy.(possession order under section 21 is not possible).
Please advise:1)Who is liable for council tax whilst protected tenancy remains active and tenant refuse to terminate their protected tenacy.
2)How can the Landlord get possesssion order and get the “ownership” of appeal property back

Can the Landlord let the property out to new suitable tenants without the lengthy process of getting a possession order?