Where for the purposes of subsection (2)(a) of section 47 above any sums have been deposited with a water undertaker by way of security for the discharge of any obligation, the undertaker shall pay interest at such rate as may be determined either—
by the undertaker with the approval of the Authority; or
in default of a determination under paragraph (a) above, by the Authority,
on every sum of 50p so deposited for every three months during which it remains in the hands of the undertaker.
An approval or determination by the Authority for the purposes of this section—
may be given or made in relation to a particular case or description of cases or generally; and
may be revoked at any time.