Section 109 of the Housing Act 1966 provides that:
(1) A housing authority may perform any of their functions under this Act outside of their functional area.
(2) Where a housing authority intends to perform a function in the functional area of another housing authority, the authority by whom the function is intended to be performed and the other authority may make and carry out an agreement in relation to the function, and where an agreement is made under this section the parties to the agreement may terminate it at any time if they so agree.
(3) The making of an agreement under this section shall be a reserved function.
A description of section 109 of the Housing Act 1966 is included in the list of Reserved Functions to be Performed by the Local Authority in Part 3 of Schedule 3 of the Local Government Reform Act 2014, which states:-
'The making of an agreement between authorities to enable a housing authority to perform any of its housing functions outside its functional area.'
I am not aware of any other statutory description of the section 109 provision.