The right to acquire on rent to mortgage terms cannot be exercised if—
it has been determined that the tenant is or was entitled to housing benefit in respect of any part of the relevant period, or
a claim for housing benefit in respect of any part of that period has been made (or is treated as having been made) by or on behalf of the tenant and has not been determined or withdrawn.
In this section " the relevant period " means the period—
beginning twelve months before the day on which the tenant claims to exercise the right to acquire on rent to mortgage terms, and
ending with the day on which the conveyance or grant is executed in pursuance of that right.