As Nick Clegg and the Liberal Democrats negotiate with David Cameron's Conservatives over the ramifications of the hung parliament, the question of proportional representation has come up - especially for the demonstrators from Take Back Parliament.

New figures from the Electoral Reform Society examine exactly how well each party would have done under different systems of PR: Alternative Vote (AV), Alternative vote plus and Single Transferable Vote (STV).

Interestingly they show that under AV - the system being negotiated and which Gordon Brown and Labour have already pledged a referendum over - the Lib Dems would only increase their seats to 79.

UPDATE: AV plus figures have been added to the dataset and table below.

UPDATE: As several posters have noted below, this is hardly an exact science. If it helps, here's the methodology from the ERS summarised:



• Our simulations should be regarded as illustrative … the picture they give is necessarily a rough one.

• We have assumed that votes cast on 6 May would have been 'first preferences'. [But] there was a considerable amount of tactical voting … secondly many people would not have voted for their preferred party on the grounds they could not win (for this reason the simulations probably underestimate support for the Green Party)

• AV and STV use preference voting (i.e. voters can rank candidates in order of preference). In our models we have used the second preference data of a ComRes poll of 26 April 2010 (fieldwork on 24/25 April 2010). This data, however, has a number of shortcomings when it comes to estimating how votes for smaller parties might transfer, and has obvious difficulties in Scotland and Wales … In the great majority of seats the simulated outcome is not particularly sensitive to the accuracy of the assumptions made on transfers.

• The polling data suggests that many voters would not wish to express a second preference, and consequently the impact of AV is not as great as other simulations have suggested.

• Our modelling of STV has used constituencies electing 3, 4 or 5 MPs.

I've pasted it in full in the comments field below - or you can get more info direct from the ERS.

The regional breakdown is below - and we should be able to get constituency-level breakdown later today.

You can download the data below - let us know what you can do with it.

• DATA: download the full datasheet

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Summary data

PR and the election 2010 result Click headings to sort VOTE SYSTEM: REGION CON LAB LIB DEM SNP PC Other FPTP: TOTALS 307 258 57 6 3 19 AV: TOTALS 281 262 79 5 3 20 AV+: TOTALS 275 234 110 9 3 19 STV: TOTALS 246 207 162 13 4 18 FPTP: London 28 38 7 FPTP: Wales 8 26 3 3 FPTP: W Midlands 33 24 2 FPTP: Scotland 1 41 11 6 FPTP: E Midlands 31 15 0 FPTP: N East 2 25 2 FPTP: S East 75 4 4 1 FPTP: N West 22 47 6 FPTP: South West 36 4 15 FPTP: Eastern 52 2 4 FPTP: York & Humber 19 32 3 FPTP: N Ireland 18 AV: London 27 39 7 AV: Wales 6 25 6 3 AV: W Midlands 31 25 2 1 AV: Scotland 1 41 12 5 AV: E Midlands 27 15 4 AV: N East 1 26 2 AV: S East 74 4 5 1 AV: N West 20 47 8 AV: South West 31 4 20 AV: Eastern 46 6 6 AV: York & Humber 17 30 7 AV: N Ireland 18 AV+: London 23 33 6 AV+: Wales 5 22 5 2 AV+: W Midlands 27 22 1 AV+: Scotland 1 35 10 4 AV+: E Midlands 23 13 3 AV+: N East 1 23 1 AV+: S East 63 3 4 1 AV+: N West 17 40 6 AV+: South West 26 3 17 AV+: Eastern 39 5 5 AV+: York & Humber 15 25 6 AV+: N Ireland 0 0 0 15 STV: London 27 28 18 STV: Wales 10 16 10 4 STV: W Midlands 26 20 13 STV: Scotland 7 28 11 13 STV: E Midlands 22 15 9 STV: N East 8 13 8 STV: S East 50 11 23 STV: N West 25 33 17 STV: South West 25 6 24 STV: Eastern 25 19 14 STV: York & Humber 21 18 15 STV: N Ireland 18



