There is no statutory process for either scenario.Subject to the agreement of both parties, any owner-occupier who wishes to sell their home to a local authority and remain in it as a tenant in the social rented sector may do so.If there is already a private tenancy in place, prior to any purchase there could be some negotiation and agreement with the sitting tenant in order to bring their private tenancy with their existing landlord to an end so that they may enter into a social tenancy when the property is purchased by the local authority.