A county council may let land acquired or appropriated by the council for small holdings for cultivation as an allotment, or to a local authority or association, being an association to which land may be let by a council under the Small Holdings and Allotments Acts, 1908 to 1919, for the purpose of being sub-let for such use: Provided that this section shall not be deemed to authorise a council to let any land held by the council under a contract of tenancy or the use of any land so held in contravention of any term or condition of the contract.