Except in so far as in any particular case any privilege or immunity is waived by the Union, officials of the Union of any category specified by it shall enjoy—
(a) immunity from suit and legal process in respect of words spoken or written and things done or omitted to be done by them in the course of the performance of their official duties;
(b) exemption from income tax in respect of emoluments received by them as officers or servants of the Union.