The requirement of locus standi of a party to a litigation is mandatory, because the legal capacity of the party to any litigation whether private or public action in relation to any specific remedy sought for has to be primarily ascertained at the threshold. In a private action the litigation is bipolar. In defining the rule of locus standi no "rigid litmus test" can be applied since broad contours of PIL are still developing apace seemingly with divergent views on several aspects of the concept of this newly developed law and discovered jurisdiction of judicial activism with far reaching change both in the nature and form of the judicial process. Writ petition by mere busybody or interloper not to be entertained. Depends on circumstances. .[ Janatha Dal vs H.S.Chowdhary AIR 1993 SC 892 = 1992 (5) JT 231=(1992) 4 SCC 305 = 1993 AIRSCW 248 = 1993 Crl LJ 600 . S.Ratnavel Pandian & K.Jayachandra Reddy (JJ)]