The local housing authority shall not entertain an application for assistance under this Part if—
unless the grant application has been refused or has been withdrawn under subsection (2) or the relevant works have been completed.
Where a person has applied for such a grant in respect of a dwelling and—
he may withdraw his application, whether or not it has been approved, if the relevant works have not been begun.
In this section "relevant works", in relation to a grant, has the same meaning as in Part XV.