Where:
(a) the employment of a contributor terminates or is terminated; and
(b) immediately after the day on which his employment terminates or is terminated, he becomes employed by the Commonwealth or by an approved authority on terms that require him to give the whole of his time to the duties of his employment;
he shall be deemed not to have ceased, by reason of that termination of his employment, to be a contributor or to be, or to be deemed to be, an employee.