The principle of immunity protects all acts which the public servant has to perform in the exercise of the functions of the Government. The purpose for which they are performed protects these acts from criminal prosecution. However, there is an exception. Where a criminal act is performed under the colour of authority but which in reality is for the public servant's own pleasure or benefit then such acts shall not be protected under the doctrine of State immunity.
If newspaper reports are to be relied upon, the CBI is basically arguing against the doctrine of precedent: 'the Supreme Court ruling in one particular case cannot be referred to as a general law.' This is not to say that there is not a practical difficulty with this second exception: whether the act was for the public servant's own pleasure or benefit is usually apparent only after a trial. This exception therefore requires the magistrate to accept a prima facie case that that is so, before taking cognizance in the absence of official sanction.
Venkatesan points out another controversy relating to impunity provisions in Kerala, where the issue is whether the Governor is bound by the advice of the Council of Ministers to refuse sanction for prosecution. Another SC precedent allowing the Governor to do so in case the Council of Ministers has not acted bona fide is in issue [M.P. Special Police Establishment v. State of M.P 2004 (8) SCC 788 -- I am only citing from the news report, have not read the case myself yet.]
While these exceptions demonstrate understandable judicial frustration with impunity provisions, it is high time our courts realise that impunity provisions are unconstitutional per se.
One also hopes that this time the PM finally has enough political authority to push through his proposal of creating a separate prosecutorial authority, independent of the CBI. (See also this previous post on this blog).