During the current referendum debate, NO campaigners have argued that AV would lead to more coalition governments.
However, the YES campaign have argued that First Past the Post (FPTP) leads to coalitions, and would do so more often in the future if kept as the UK electing system.
'Yes to fairer votes': "Voters delivered a hung parliament in 2010 under First Past the Post, and not for the first time."
'No to AV': "AV leads to more hung parliaments, backroom deals and broken promises like the Lib Dem tuition fees U-turn. Instead of the voters choosing the government, politicians would hold power. Under AV, the only vote that really counts is Nick Clegg's."
"Our current system tends to create strong, accountable governments and means that coalitions are uncommon, with no horse-trading by politicians behind the scenes. AV isn't proportional and it leads to more backroom political deals, the worst of both worlds."
The current trends to multi-party democracy in the UK and the regional fragmentation of party support across the UK, make it more likely that no government will gain a majority in future elections, whether under AV or FPTP.
Neither of these trends are due to FPTP or AV.
When a party does win a strong majority, they are likely to gain more seats under AV than under FPTP, as would have happened in 1997.
However, when elections are closer, AV would increase the likelihood of coalition government. This is shown in an authoritative British Electoral Study simulation of what the 2010 general election results would have been under AV. It says the results indicate: "that the Conservatives would have won 22 fewer seats than they actually obtained under FPTP and that Labour would have won 10 fewer. The Liberal Democrats would have been clear net gainers, increasing their representation from 57 seats to 89."
Looking further back at the BES work, a briefing from the Political Studies Association makes the point that had AV been used in previous elections, the only result that would have possibly been different under AV would have been the 1992 vote.
However the report briefing acknowledges: "By boosting the Liberal Democrats, however, AV does increase the likelihood of hung parliaments a little."
International comparisons are also contentious. The example of Australia is frequently cited as proof that AV would not frequently deliver coalitions.
However, as highlighted on Channel 4's Factcheck, the Australian National and Liberal parties have been operating in coalition since 1992. It is by viewing this alliance as a single party that Australia can be seen to have had few hung parliaments.
The Institute for Public Policy Research (IPPR), a think tank, have researched a report that raising questions of ability of First Past the Post to produce majority governments in the UK.
It says that: "as the outcome of the 2010 general election proves, FPTP can no longer claim to guarantee 'strong single-party government'.The report argues that this is because of the rise of minority parties, and falling support for Labour and the Conservatives.
They say that: "If future parliaments are likely to include at least 85 MPs from parties other than Labour or the Conservatives, then in order to secure an overall majority one of the main parties needs to secure at least 86 more seats than its rival (Bogdanor forthcoming 2011). But... this has happened in fewer than half — seven — of the 18 general elections since the war... And achieving a majority of only 20 seats— which it could reasonably be argued is the minimum a party needs to govern securely — would entail one party having to win over 100 seats more than the second-place party, a result which has occurred even less frequently: since the war, only in 1945, 1983, 2001 and 2005."
Indeed, the IPPR report also notes that other Westminster model systems are seeing a very similar trend towards multi-party politics.
As well as the rise of third parties in the UK, the fragmentation of party support across the UK is a further reason for the increased likelihood of no party gaining a majority in UK national elections.
Both these dynamics are relatively recent in British electoral history, and both are evolving issues. Therefore, how they impact on electoral outcomes under either AV or FPTP is unlikely to stay constant.