The effect of Britain's new major parties

At the last general election in 2010, the three main parties had 88% of the vote.  That figure for the same three parties is now down to 72%, as three new parties have come to the forefront of British politics.

If the UK used a form of proportional representation, we would expect the UK Independence Party and the Green Party to have dozens of seats in the House of Commons.  However, with the first-past-the-post system that we have, neither of these parties is expected to get into the double digits on current projections.

Even though these representations of these two parties are expected to be tiny after the election, their uprisings are still having an impact on the balance of power across the UK.

Scottish National Party

Since last year's independence referendum, support for the Scottish National Party has more than doubled, and most seats in Scotland are expected to go to the SNP.  It came as the party shed its independence movement post-referendum and pledged to fight for the further devolution which has been promised by the other three main parties.

How seat projections in Scotland have changed since the referendum.

How seat projections in the entire UK have changed since the referendum.

Of course, when the SNP advances to this extent, the only party that stands to lose is the Labour party.  Before the referendum, Labour was looking at 350 seats in the UK (including 40 in Scotland), which would be a certain overall majority even when adjusting for the margin of error.  Now, they are looking at a single-figure seat count in Scotland, and around 300 in the entire UK.  This all but rules out the possibility of an overall majority in parliament.

But even if we remove the effect of the SNP, a Labour majority would not be assured.  When you look at the rest of the UK since the referendum, Labour support has dropped by about 20 seats.  Even if we assume Scotland stayed the same since then (which it did from the election and the referendum, though not at all points in between), the resulting Labour majority would only be around 10 seats, which leaves a hung parliament well within the margin of error.  Even if that majority is realised, it's not nearly enough to govern successfully for an entire parliament.

How seat projections have changed in England, Wales and NI since the referendum.

Overall, if not for the swing to the SNP, Labour would be looking at around a 50:50 chance of securing an overall majority, all else being equal.  Even if they don't secure an outright majority, SDLP support from Northern Ireland would give them enough seats that they can govern effectively.

UK Independence Party

UKIP support first hit 10% in the autumn of 2012, overtaking the Liberal Democrats for the first time.  This came as the Eurozone debt crisis was reaching its climax and net migration to the UK was increasing, leading to a rise in Euroskepticism in the country.  Even though the Conservatives announced an in/out referendum at the start of 2013, it has done little to stem the swing from them to UKIP.

Not all of the swing to UKIP is coming from the Conservatives.  Recent polls show that those planning to vote for UKIP today voted as follows in 2010:

• 36% voted for the Conservatives
• 12% voted for Labour
• 10% voted for the Liberal Democrats
• 42% voted for someone else

If we were to redistribute the UKIP vote based on the above, we would see the Conservatives move ahead of Labour, picking up around 20 seats at Labour's expense and 10 at the expense of the Lib Dems.  It would shift the balance of power to 99% odds of Labour being the largest party to 94% odds of Conservatives being the largest party.

After the swing to UKIP is removed and returned to their 2010 parties.

Overall, if not for the swing to UKIP, the Conservatives would be looking at becoming the largest party in the House of Commons.  That said, it would still face difficulty forming a coalition that could successfully govern, as the SNP would never support a Conservative government and the Lib Dems wouldn't have enough seats to push them over the line.

Green Party

As unpopularity with the Liberal Democrats has continued to grow, much of the protest vote that used to go to them is now going to the Green party.  However, not all of their vote is coming from the Lib Dems, but rather, according to the same polls as used for the UKIP figures:

• 35% from the Liberal Democrats
• 14% from Labour
• 5% from the Conservatives
• 46% from elsewhere

If the Green vote were to be redistributed accordingly, Labour would gain about 10 seats, and the LibDems around 5.  That said, it wouldn't be enough for Labour to gain a realistic prospect of an overall majority.

After the swing to Green is removed and returned to their 2010 parties.

Overall, the effect of the Green Party is negligible.

In summary, if you took out the effects of these three parties, the result would approximately net out, since the seats that Labour is losing because of the SNP is around the same as what the Conservatives are losing because of UKIP.  We would still be looking at a hung parliament with Labour as the largest party, with the Liberal Democrats still not able to hold the balance of power on their own.  Similar to the situation at the moment, a second election in 2015 or early 2016 could not be ruled out.

It's hard to say exactly how many seats any of the new major parties will get, simply because unlike with the established parties, it's hard to know the specific areas where they'll do well and in which seats they will target their resources.  But with seven parties to be invited to this election's debates, and with swings going all over the place, it's safe to say that the swingometer that we've been using for over fifty years is simply not going to be enough this year.