(1) Any citizen of India who by naturalisation, registration otherwise voluntarily acquires, or has at any time between the 26th January, 1950 and the commencement of this Act, voluntarily acquired, the citizenship of another country shall, upon such acquisition or, as the case may be, such commencement, cease to be a citizen of India:
     Provided that nothing in this sub-section shall apply to a citizen of India who, during any war in which India may be engaged, voluntarily acquires the citizenship of another country, until the Central Government otherwise directs.
     (2) If any question arises as to whether, when or how any ¹ [citizen of India] has acquired the citizenship of another country, it shall be determined by such authority, in such manner, and having regard to such rules of evidence, as may be prescribed in this behalf.