This article explores the concepts of determining what takes to win a Westminster seat in numeric terms, against the national background of opinion polls and public mood. It does not attempt to take into account any local factors, such as suspected corrupt or inept incumbents, particularly high-profile challengers or the effectiveness of any local branches. And, it looks at the numbers from the point of view of the different types of parties: the one in government, the opposition and minor parties.

In order to protect the innocent, and for the sake of maintaining objectivity in our analysis, we’ll call these parties Party A, B, C and D. Parties A and B have traditionally ping-ponged between being the government and main opposition but Party A is currently in power, Party C has been the largest minor party so far, and might have been part of coalitions in the past or present, while Party D is the “new kid on the block” challenging on a popular set of issues. Any resemblance to real parties is completely coincidental.

We will look at a constituency of 75,000 voters, where turnout is normally 66.7% = 50,000. So, let’s take a safe government party seat, where Party A had a whopping majority at the last election:

Safe Gov’t

Last Election

Party B strengthens

Party C Strengthens

Party D Strengthens

Seat

Votes

%

Swing to B

Votes

Swing to C

Votes

Swing to D

Votes

Party A

27,500

55%

25%

20,625

31%

18,975

32.5%

18,562

Party B

12,500

25%

 

20,626

20%

10,000

20%

10,000

Party C

7,500

15%

13%

6,562

 

19,000

20%

6,000

Party D

2,500

5%

13%

2,187

20%

2,025

 

18,563

Non-Voters

25,000

 

0%

25,000

0%

25,000

12.5%

21,875

We will also assume that the government is unpopular, so what will it take for the opposition Party B to unseat them in this constituency? The answer is a pretty large swing of 25% from A, plus picking up some votes from each of C and D.  It’s a pretty big task, mostly dependant on how awful the government is, and how attractive the opposition’s policies look.

What about Party C? Their task looks even more formidable, needing 31% from A, and 20% from the others.

However, Party D has a secret weapon – their policies are so radically different and popular that they can attract votes from about an eighth of the non-voters. They can achieve a level footing with the stronger minor party through that appeal to those non-voters.

How does it look when opposition Party B hold the seat?

Safe Opp’n

Last Election

Party A strengthens

Party C Strengthens

Party D Strengthens

Seat

Votes

%

Swing to A

Votes

Swing to C

Votes

Swing to D

Votes

Party A

12,500

25%

 

20,627

39.0%

7,625

40.0%

7,499

Party B

27,500

55%

25%

20,624

26.6%

20,174

27.0%

20,075

Party C

7,500

15%

13%

6,562

 

20,176

27.0%

5,475

Party D

2,500

5%

13%

2,187

19%

2,025

 

20,076

Non-Voters

25,000

 

0%

25,000

0%

25,000

12.5%

21,875

If the government were doing badly, Party B would increase their majority, but let’s say there is a fluke result – they would need to reverse the swings from the previous example. For minority Parties C and D to win, they would have to try even harder, pulling 39-40% of the government party’s vote and 27% of the others.

Now it starts to get more interesting. What about a 2-way marginal, both government and main opposition parties almost having the same share of the vote?

2-way

Last Election

Party B strengthens

Party C Strengthens

Party D Strengthens

Marginal

Votes

%

Swing to B

Votes

Swing to C

Votes

Swing to D

Votes

Party A

20,000

40%

1%

19,800

20%

16,000

22.2%

15,570

Party B

19,500

39%

 

19,807

20%

15,600

22.2%

15,180

Party C

8,000

16%

1%

7,919

 

16,150

15%

6,800

Party D

2,500

5%

1%

2,474

10%

2,250

 

15,575

Non-Voters

25,000

 

0%

25,000

0%

25,000

12.5%

21,875

For Party B to win, it would only take a slither of a swing for them to do it – a dead “cert” if government were performing poorly. But, for Parties C or D to win, they do not need anywhere near the amount of effort that they did in a safe seat, stealing votes from both main parties, and off each other.

And finally, let’s look at a 3-way marginal – rare, but there are instances:

3-way Marginal

Last Election

Party B strengthens

Party C Strengthens

Party D Strengthens

Votes

%

Swing to B

Votes

Swing to C

Votes

Swing to D

Votes

Party A

16,500

33%

1%

16,335

2%

16,170

20%

13,200

Party B

16,000

32%

 

16,342

2%

15,679

20%

12,800

Party C

15,500

31%

1%

15,344

 

16,171

12.5%

13,562

Party D

2,000

4%

1%

1,979

1%

1,980

 

13,563

Non-Voters

25,000

 

0%

25,000

0%

25,000

12.5%

21,875

In this case, any one of the three formerly stronger contenders would only need a tiny swing to take the seat. And even “Party D” would not need as many votes to win the seat by a whisker, helped along as always by the non-voters returning to voting because of them.

Naturally, I’m sure you’ve guessed that Conservative and Labour are portrayed as Party A and Party B, Party C is meant to be the Liberal Democrats, and Party D is UKIP. The simplistic analysis above does not account for the way the Liberal Democrat vote has already been decimated by their voters deserting to mainly Labour in 2010/11 with some to the Conservatives and Greens.

Conclusion: if you want to detect a good UKIP seat to contest, or want to know where to place your resources for the best outcome, look for those with a very strong Liberal Democrat majority in 2010, or those that are Labour/Conservative marginals – they are, all things equal, the most fertile battlegrounds for gaining UKIP Westminster seats.

 

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