The British public is finally being offered a referendum on electoral reform because the faults of the Westminster system are all too apparent. The way it gives so many more seats in relation to votes to leading parties and squeezes out third-placed and smaller ones; the way if offers constituents only one Member of Parliament to represent them, despite the residents' diversity; the way some winners can get their seat with only a handful of votes more than the next candidate, while others can hold on to theirs for decades due to an in-built social majority of their constituency's residents; and the way our Single-Member Majoritarian system (FPTP) can give the leading party overwhelming dominance of parliament and government  –  such defects undermine confidence in the parliamentary system. 

Does this mean that critics of FPTP should embrace a change to the Alternative Vote? Unfortunately not. Alone in the world, Papua New Guinea (PNG) and Australia use it for their national parliaments. It has worked well in Papua because in polities that are highly fragmented along ethnic and tribal lines, AV prevents candidates from behaving in an overly partisan way, making them seek support beyond their own communal base in order to gain the 2nd preference votes and get elected with an overall majority. But this is the very opposite of Britain's situation, where three nationwide parties stand accused of becoming increasingly similar, and a worrying number of potential voters abstain from deciding between them. AV is said by specialists to be the best system for promoting centrist politics, just what reformers in Britain wish to avoid.

By now we all know that those little diagrams on websites are a misleading simplification of the AV count. Do we all get our 2nd and subsequent preferences counted towards the outcome? No. Do all preferences even get counted? No. Will Labour and Conservative voters be able to transfer their 2nd choice to the Lib Dems, so as to prevent each other's rivals from winning? Not usually – only if the Lib Dems have already beaten them by coming top or runner-up. In sum, a large majority of voters will never have their 2nd choices counted.

If the reason for reform is to increase competition between the old parties and help new ones, AV does the opposite. Whichever party comes third-place in a constituency is the only mainstream option whose ballots will have their 2nd and subsequent preferences counted along with those of the small and fringe parties. What the Lib Dems are probably hoping for is that, as their candidates frequently end up in third position, their voters will have the casting vote using their 2nd preferences to determine the winner, with this pattern repeating itself in numerous constituencies.

But if third-placed LibDems become kingmakers with their 2nd preferences, both Labour and Conservatives will want to develop alliances with them, whether voiced or whispered, and policy differences will blur even further. Instead of going all out to persuade voters to back them on the grounds of their difference from other parties, candidates would have to make broadly-based appeals to attract more 2nd preferences, rather than focusing on narrower issues, as explained by the online Electoral Knowledge Network. More hot air, fewer specifics.

In fact, choosing between so many poorly defined candidates confuses people so much that Australian parties issue voter guides telling their supporters who to vote for in their 2nd and subsequent preferences – this shows how AV pushes parties into constituency alliances that may actually be undesirable at national level. Imagine the British scenario in which the candidate from Party A has to convey the message, endorsed by the party, "Vote for me, but if you must vote for Party B, remember I'm not that different, so you can put me down as your 2nd preference", while Party A's sitting MP in the next constituency might have to suggest the opposite to Party C voters if their candidate is likely to come third: "I'm not so different from Party C, so give me your 2nd preference". A level of political incoherence likely to increase the electorate's disdain for politics, and an uncomfortable situation for MPs.

As to opening up parliament to more parties, AV does the opposite: it concentrates the vote on the two main parties, since the winner needs a bigger majority than under FPTP. In Australia, the two leading parties got 82% of the votes on 1st preferences alone, while the Green's 2nd preferences got transferred mainly to Labor, leaving the Greens with only one MP.

UK Green Party take note: with 1% of the national vote, you got one MP under FPTP. The Australian Greens got nearly 12% of the national vote, but only one MP. Under AV, Green parties cannot obtain a seat with a simple plurality, yet getting a majority is far too difficult, even if they were twelve times more popular than now, because a party must come top or runner-up on 1st preferences in a constituency before benefiting from any 2nd choices.

As to electoral reformers' desire to increase proportionality, AV does not offer this, as it remains a Majoritarian single-winner system. It does not offer strong majorities either. In the recent Australian election Labor got 37% and the Liberal Coalition got 44% of the vote on 1st preferences but ended up with the same number of seats each. Adding in the extra preferences, they came neck-and-neck, but with no change of seats and Labor had to reach for independents to form a government with a razor-thin majority. This means AV neither gives a significant increase in seats to the leading party (desirable for government stability), nor produces a more proportional outcome (as under PR). Instead, it entrenches the two-party system.

Advocates of a greater representation of women in parliament should give up any illusion that AV per se will help. Though Australia with nearly 25% of women is ranked 41st in the world, above the UK (22% and in 53rd place), Papua New Guinea has only one female MP (0.9%). By comparison, New Zealand with a Mixed Member Proportional system ranks 17th in the world with nearly 34% of MPs being women.

In terms of announcing the results, under AV election night could be a flop, because the count would not be in on time. With, say, ten candidates running, constituency tellers used to counting a turnout of 50,000 voters could be faced with half a million choices! Perhaps it's just as just as well they are not actually going to count most of them, but they still have to shuffle around the ballots to small parties to find enough 2nd, 3rd, 4th etc preferences to push a candidate over 25,000 votes to get the seat.

As to the alternatives to AV, the Scottish and Welsh FPTP with their tiers of Additional Members elected on a different basis, and Germany too, have the merit of achieving greater proportionality of seats gained in the legislative assembly. But to increase the presence of women it was necessary to impose strict gender balance rules on the parties because the system itself doesn’t deliver it. Two tier (Additional or Mixed Member) systems thus constitute an improvement over FPTP and AV, but at the cost of creating two types of MP (which leads to tensions), and having extremely complicated vote-counting systems.

To institute a top tier system at Westminster, the total number of MPs would have to rise considerably or the number of Single Member constituencies be reduced by nearly half – in other words a complete re-design that incumbent MPs would not vote for. The same problem would affect any planned adoption of an existing Proportional Representation with a Party lists of candidates, since large multi-member constituencies would have to be created, and most MPs fear the loss of their links with their current relatively small ones.

The best bet for reformers would be to advocate a new system that maintained the MPs' links with the small area of the present constituencies, while at the same time allocating seats in a more proportional way to parties, such as by distributing them across a group of constituencies – a multi-member district – so as to create proportionality within the group/district, while keeping the candidate selection and campaigning and representation constituency-based. A more proportional seat allocation would put an end to the current vast electoral 'deserts' where there are either no Labour or no Conservative MPs to represent supporters who voted for losing candidates. A hybrid system combining moderate PR with constituency links for MPs would solve many electoral defects of both systems and renovate Westminster parliamentary life without requiring the resignation or re-election of incumbent MPs.

The full proposal for a new electoral system for Westminster, with its implementation guide, is available for scrutiny and comment here.

Dr Monica Threlfall is Reader in European Politics at the Institute for the Study of European Transformations.