What if Proportional Representation had been used in the 2010 UK General Election?

With the vote in the commons and hopefully (for the Lib Dems) referendum on switching to the AV system for elections some are calling that it does not go far enough.

But as question that is the title of this post asks... what if PR had been used in 2010?

Well as PR is based on percentage of the vote won I'd best give the result for those who would qualify assuming that 1% was required to win seats.

Votes
Conservative - 36.1% (36)
Labour - 29%
Lib Dem - 23%
UKIP - 3.1%
BNP - 1.9%
SNP - 1.7%
Green - 1%
Total - 95.8% of vote qualifies for seats

Seats (based on %)
Conservative - 234.65
Labour - 188.5
Lib Dem - 149.5
UKIP - 20.15
BNP - 12.35
SNP - 11.05
Green - 6.5
Total 622.7

Time for a Question within a Question, when deciding actual seats, do I simply count every actual seat won and ignore point places or do I round up and down accordingly

1)If I were to ignore decimal places for seats the final result would be

Con - 234
Lab - 188
Lid - 149
UKIP - 20
BNP - 12
SNP - 11
Gre - 6
Result - 620 seats - Hung Parliament - Cons lacking 77 seats for majority of 1

Almost poetically this result means that a Lib/Lab coalition would have been numerically possible as they would equal 337

2)If however I were to round up we get another question..do we round up the percent of votes cast for everyone? Then a party would need 0.5% of the vote to qualify for a percent of the seats.

2a) if we take it that a party need 1% to qualify for seats but then were rounded up

Votes/share/Seats
Cons - 36.1% - 36% - 234
Lab - 29% - 29% - 188
Lib - 23% - 23% - 149
UKIP - 3.1% - 3% - 19.5 seats = 20
BNP - 1.9% - 2% - 13
SNP - 1.7% - 2% - 13
Gre - 1% - 1% - 6.5 seats = 7
Total seats - 624 - Hung Parliament - Cons lack 79 seats for majority of 1

Really only slight differences to bottom of the table that increase the number of seats and the number of seats needed for a majority.

2b) If rounding up as used throughout the whole process 3 more parties would qualify for seats

Sinn Fein - 0.6% of Vote
DUP - 0.6% of Vote
Plaid Cymru - 0.6% of Vote

Each would be rounded up to 1% and would then qualify for the same 7 seats as the Greens meaning the final table with rounding would look something like this;

Con - 234
Lab - 188
Lib - 149
UKIP - 20
BNP - 13
SNP - 13
Gre - 7
DUP - 7
Sinn - 7
Cym - 7

Total Seats - 645 - Hung Parliament - 323 needed for majority

These seat numbers are of course based on the idea that the Commons remained at 650 going into the election. It would most likely have to be decided how many seats would be in the commons prior to any election.

What I find most interesting is just how close the Lib Dems and Labour really are.

So hopefully this has given you an idea on how the current parliament would have looked like had PR been used.