The resignation of two MSPs from the governing SNP in the Scottish Parliament earlier this week over NATO membership is causing more than just a headache for party leader Alex Salmond. It is also exposing a troublesome facet of the mixed member proportional system (MMP)[1] that is used to elect Members of the Scottish Parliament.

A quick briefing on just what MMP is. MMP systems elect two types of member: constituency members, who receive a direct mandate by gaining sufficient votes from within a constituency, and list members, who come into parliament via their position on a regional party list. This list exists to compensate for those votes that were cast for a party where they didn’t win constituency seats. The two MSPs in question, John Finnie and Jean Urquhart, were regional list MSPs (see the ACE Electoral Knowledge Network page on MMP for more).

The existence of list members serves to achieve greater proportionality between votes cast and party representation in parliament. But the implication here is that without allegiance to their party, these members have no mandate to continue to sit in Parliament at all. Senior SNP member Christine Grahame yesterday said the very same, and called on Finnie and Urquhart to resign from Parliament: “the principle here”, she stated, “is you’re here simply to represent a number of SNP votes. You’re no longer in the SNP, you should resign”.

The counter-case looks weak. The SNP code of conduct, for one, is clear on the matter. It states that “any member resigning from a party group at any level of government owes a duty to the party also to resign as a member of the local authority or parliament to which he/she was elected as a party candidate”.

How has this quandary been dealt with in other countries which use MMP?

While floor crossing (the practice of members switching party mid-Parliament) is generally not permitted in purely proportional systems (list PR), it tends to be permitted in MMP systems for the constituency MPs but not the list MPs.

In Germany, while the practice is permitted in law, it has only happened on two occasions in the last fifty years, largely because of the significant negative public perception of party change as an affront to the voter’s preference.[2]

The floor crossing phenomenon became rife in New Zealand following the switch from first-past-the-post to MMP in 1993. It prompted adoption of legislation in 2001 requiring party lists MPs to resign from parliament if they had resigned from the party under which they were elected.

But the problem has been raised even in the UK’s first past the post system. Last November Conservative Westminster MP Chris Skidmore presented a 10-minute order in the Commons which sought to oblige any member who voluntarily decides to change party to resign and fight a by-election. It raised the age-old Burkean questions about what exactly it is that MPs represent: are they delegates acting on behalf of the electorate or rather trustees of the electorate acting according to their best judgment? Party loyalty and discipline only further muddy the waters. However, that debate is less pertinent in the case of the list MP. With no constituency, their legitimacy clearly derives from their party and they cannot lay claim to an individual mandate.

As the Scottish Parliament stands out as a beacon for alternatives to first past the post in the UK, it is worth taking seriously the need to resolve its finer intricacies lest the floor-crossers become an endemic problem.