While an MP might owe his or her place in parliament, or even cabinet, not due to patronage from above, but because he was an NUM MP, or had
backing from the public sector unions, or the London Labour Party etc, s / he could enter into those discussions pre-vote from a position of real stregnth.
From the sound of the NS Act, it
resulted from public sector unions being concerned about outsourcing data processing (which is what the unsuccessful complaints in BC and ON were about.)