A professor and supporter of the MMP process says it isn't fair to say Winston Peters has thwarted the system.

New Zealand has elected a Government under the MMP system since 1996 but the process hasn't come under scrutiny recently because of the John Key-led National majority wins.

Public Policy Professor Jonathan Boston says [told Mike Hosking] says the last few weeks have been a negative part of MMP but that's not just because of Mr Peters.

"If National or Labour had refused to negotiate with him, his bargaining position would obviously been dramatically weakened. It's not just his decision in this, there's lots of other players making decisions."