With the unprecedented closeness and unpredictability of the next general election, there has been a lot of speculation about which parties may be able to do business together in the event of coalition negotiations, following another hung parliament. The SNP have ruled out the possibility of doing a deal with the Conservatives, but what other parties look like they may be able to do a deal based on the way that they vote? With potentially 10 or more seats in the next parliament, could the DUP act as kingmakers, or are they too far apart ideologically from either Labour or the Tories to realistically have a choice of coalition partners?

As suggested by Mick, I took an extract of voting data from the Public Whip, who have a fantastic database of how MPs and Lords vote on various issues. I then went through all 114 votes since the 2014 summer recess, and assigned an ideology score for each Aye or No vote. My scores are obviously and necessarily subjective, and can be found in a Google spreadsheet here. Even if you disagree with some of the scores on individual votes, they should offer a meaningful picture when aggregated together.

I have used the two-dimensional political ideology map, as invented by David Nolan and popularized by The Political Compass, which maps political belief in two dimensions. Free market beliefs are on the x-axis, with those on the right being those who believe in the principles of free markets, with socialist beliefs to the left. The y-axis represents authoritarian beliefs, with those advocating civil liberties at the bottom and people with a more authoritarian outlook at the top.

Traditionally political discourse runs from the top right quadrant to the bottom left. Consider Margaret Thatcher, who combined strong free market principles with a belief in a strong government presence in personal and moral matters. Socialists would tend to hold the opposite views, with a belief in government intervention in economic matters (e.g. a minimum wage), but non-intervention in personal matters. People in the top left quadrant would be authoritarian economic populists such as Robert Mugabe, and those in the bottom right would be libertarians, such as former US Republican presidential candidate Ron Paul.

I looked at Northern Ireland MPs first. Obviously, as Sinn Féin do not take their seats at Westminster, it is not possible to compute a score for their MPs. The ideological position of the remaining Northern Ireland MPs can be found in the chart below.

The three SDLP MPs and the Alliance MP Naomi Long are clustered closely together on the economic left and civil libertarian end of the spectrum. The independent Sylvia Hermon is slightly to the right and upwards of this cluster. However, there is a wide spectrum of ideological voting patterns amongst the DUP parliamentary party. With his votes on subjects such as the minimum wage, the bedroom tax, taxation and spending cuts, Nigel Dodds of the DUP is to the economic left of Mark Durkan based on the last six months of voting patterns. Other DUP MPs’ votes on issues such as healthcare and smoking put them towards the economic centre.

However, the origin of the graph (the point with 0 on both the x-axis and y-axis) is towards the top right of the Northern Ireland graph, which suggests that Northern Ireland MPs may skew to the left economically. To find out how Northern Ireland MPs compare to MPs from Great Britain, it is necessary to have a see where they sit on the overall spectrum of voting behaviour. The following chart shows the ideological voting scores of all MPs who have voted since September 2014.

As you would expect, the Conservative party are clustered in the top right quadrant of the graph, and the Labour party are clustered in the bottom left. The Liberal Democrats, whilst obviously close to the Conservatives as they are in a coalition government together, have a clearly differentiated space in the ideological spectrum, being clearly to the economic left and the civil libertarian left of the Conservatives.

If you take the ideological spectrum as running from the bottom left to the top right, then it becomes apparent the implausibility of Plaid Cymru, the SNP or the Greens doing any sort of business with the Tories. Along with George Galloway of Respect, they sit clearly on Labour’s left flank. Interestingly the two UKIP MPs vote in a similar fashion to the Liberal Democrats, suggesting that they may not be as far apart on bread and butter domestic issues as they would both claim. Possibly the idea of a blue-orange-purple coalition is not as far-fetched as it seems.

In context with all UK MPs, it would appear that the DUP could indeed swing both ways in coalition negotiations. They have a centrist outlook economically, and indeed seem to be the only politicians in Westminster who sit in between the Labour and Conservative camps. Sylvia Hermon sits in a unique position on the political spectrum, sitting slightly to the right of Labour but massively to the left of the Conservatives; it is not hard to see why she did not see the UCU-NF experiment as being for her.

With UKIP firmly in the right-wing camp, and the SNP, PC, the SDLP, the Greens and the Alliance Party in the left leaning camp, the fact that the Lib Dems or the DUP could jump either way could give them power far larger than their number of MPs would suggest. When it comes to coalition building, with the magic numbers in front of me, you can’t mistake ideology.