(1) The Central Government may, if it is satisfied at any times that by reason of the gravity of the situation it is necessary so to do, by order-
(a) cancel, either generally or in relation to a specified class of qualified persons, all postponement certificates in force at the date of the order, and
(b) abrogate, either generally or in relation to a specified class of qualified persons, any right to apply for the grant of a postponement certificate and any right to appeal from the refusal to grant such a certificate, and may, by order, vary or revoke any order in force under this section, without prejudice however to the previous effect of that order.