Electoral Act 1968, 116

A petitioncomplaining of an undue return or an undue election of a Member for anyconstituency by reason of want of qualification or by reason ofdisqualification, corrupt or illegal practice, irregularity, or by reason ofany other cause whatsoever, may be presented to the HighCourt by.

(a)       a voter in that constituency; or

(b)       any person who was a candidate at such election:

Providedthat a petitioner shall, before lodging his petition with the Registrar of theHigh Court, afford every person, other than the Memberwhose election or qualification is complained of(hereinafter referred to as 'the respondent'), who was a candidate atthe election to which the petition relates an opportunity of becoming aparty to the petition as a co-petitioner.

http://aceproject.org/regions-en/eisa/BW/Electoral%20Act%201968.pdf