Critics of referendums often argue that the electorate are as likely to vote based on their attitude to the government as on the matter at hand. The reality, however, is that no political decision is ever made in a vacuum. The wider context can be decisive, in parliamentary votes as much as in popular ones.

With that in mind, it is as well to be clear about what the likely impact of the referendum result will be on the coalition. At the start of the year, David Cameron resisted pressure to attack Nick Clegg, concerned about shoring up his coalition partners. That has changed in recent months as it became clearer what a yes vote could mean for Cameron’s own position in the Conservative Party.

The result has been growing friction between the coalition partners. Most cynically, the Tory-dominated No2AV has resorted to attacking Clegg over his support for Tory policies.

The underlying reasoning was explained by one leading Tory to Iain Martin, a key chronicler of the party’s thinking on the referendum:

“It will be Labour voters who decide the result of the referendum. If they think that the way to bash the government and spite David Cameron is to vote Yes to AV then they’ll do so. On the other hand if they are persuaded to see a Yes vote as a vote for Clegg and what he wants then the result could be very different.”

Recent opinion polls suggest that strategy is succeeding. If so it will reinforce two key facets of the current political situation that have favoured the Tories. The first of these is the tendency for Clegg to become a lightning rod for discontent with the coalition. The second related factor is the continual over-estimation of David Cameron by his opponents.

Why Cameron is weaker than he appears

From the moment he defeated David Davis (under a run-off voting system), Cameron became the Prime Minister in waiting in the eyes of much of the media. Yet his path to Downing Street was never as smooth as that image suggested.

Cameron was supposed to be the ‘heir to Blair’ who would detoxify the Tory brand and lead a new generation of A-list candidates to take back the centre-ground of British politics. Yet the polls throughout the last Parliament showed an electorate unwilling to ‘seal the deal’. The Conservative election campaign itself would be dismissed by many Tory commentators as a shambles. Cameron’s signature idea, the Big Society, failed to resonate, and his thunder was stolen by Nick Clegg during the TV debates.

When the votes were counted, Cameron emerged as the heir to neither Blair nor Thatcher. His share of the vote was closer to that of Neil Kinnock in 1992 than to that achieved by John Major. The closest comparison was with Edward Heath in the two elections of 1974.

When the Lib Dems opened negotiations with Labour, Cameron feared he might be looking at another term as opposition leader. That was a particularly ominous prospect because of his weakened position within his own parliamentary party. Two-thirds of his favoured A-listers had failed to get elected.

What happened next was crucial. Cameron offered the Lib Dems a referendum on the Alternative Vote, telling his own party that Labour had offered AV without a referendum. It would later emerge that this was untrue, but by then Cameron had become Prime Minister, securing his leadership at the risk of an electoral reform opposed by most of his party.

With the Orange Bookers replacing the A-listers, Cameron was now able to lead the centre-right government he had envisaged. However, the coalition also sealed his failure to transform the Tory party into that centre-right force. The Orange Bookers now occupy that space, while the Tories, in seeking to differentiate themselves within the coalition, are reverting to the territory they occupied under Cameron’s predecessors.

One result of this has been to revive the Tories’ own latent class tensions. Cameron is the first truly upper-class Tory leader since Alec Douglas-Home, and his mistakes look increasingly like a reversion the kind of aristocratic dilettantism that was swept aside following Mrs Thatcher’s defeat of William Whitelaw. Seen in that light, Cameron’s hands off approach to his Ministers looks like no more than patrician indolence, particularly when it is combined with a policy of selective loyalty to his subordinates that first became visible during the expenses crisis.

For many Tories, a Yes vote in the referendum could well be the straw that breaks the camel’s back. One MP told Iain Martin:

“Losing FPTP would be a disaster for the Tory party on a grand scale. Defeat on AV means Cameron would be toast. I think Number 10 has just started to work this out.”

ConHome’s Tim Montgomerie has warned:

 "if he loses this, he is not only the guy who lost the election he shouldn't have lost, but he has made it harder for Tories to ever win again. And that is the worst thing a leader can do to his party – to change the rules of the game against the interests of his own party. The price of Cameron's leadership is getting quite high."

Yet many on the left appear oblivious to the high stakes for Cameron. In that respect, the referendum campaign has arguably vindicated the judgement of Sunder Katwala last December:

"One sometimes hears the accusation that the Tories approach to power suggests that they think they are born to rule misses the mark. They are much less certain than they appear. The bigger problem is with the rest of us - and how our deference in expecting to see the Tories govern distorts political perceptions."

First Past the Post, the Conservative Party and David Cameron’s leadership are all products of a culture of deferential democracy. Now more than ever, the survival of that culture depends on the acquiescence of Labour voters.  If they choose to vote Yes, they have it in their power to deal a historic blow to the Tories.

Why Nick Clegg is not as vulnerable as he seems

It is clear that a no vote on 5 May will leave the Liberal Democrats in a weaker position. Lib Dem activists and supporters will question more than ever the wisdom behind entering into the coalition. There were two practical arguments for entering into this tough coalition for many Lib Dems. One was to show they were a ‘serious’ party that could get things done, the other was the chance to change to the voting system which would help prize open the two party system for good. Losing this referendum would undermine both of these arguments and it is not difficult to envisage the Lib Dems sinking further in the polls as a result of a no vote.

That is unlikely to manifest itself into a campaign to leave the government though. The Liberal Democrat Parliamentary party has a lower proportion of backbenchers than the Conservatives and therefore have a greater incentive to stay loyal. The tuition fees vote showed that to be a powerful factor reinforcing the dominance of the right-wing Orange Book faction.

The grouping within the Liberal Democrats that have found the policy direction of the government most unpalatable has been the Social Liberals (the centre-left). However, they have been slow to mobilise, having been blindsided by the rise of the Orange Bookers and the coalition. They are strongest at grassroots level, as seen through their conference motion calling on the government to amend the Health and Social Care bill.

Yet the Liberal Democrats are notoriously un-factional and still remain faithful to the party. With the Orange Bookers holding powerful government positions, the Social Liberals are a long way from bringing down the coalition, even if they wanted to.

In the 2010 General Election the Lib Dems could only win 57 seats on 23 per cent of the popular vote. The Lib Dems, social liberals included will not want a snap election under first past the post when they will probably be polling below their current 15 per cent.

In fact a no vote would lock the Lib Dems into the coalition more tightly than ever before. The government’s policy programme suggests they are already in it for the long haul. The front loading of public service cuts is the prime example of this. It is not difficult to see why, the coalition are banking on the hope that the economy will bounce back and the painful memories of public sector cuts would have subsided before they begin their re-election campaign.

As Sunder Katwala has suggested "A no vote to punish Clegg and the Liberal Democrats will be a yes vote to George Osborne's plans for his 2015 election campaign”.

We can already foresee what the 2015 Conservative election strategy will look like. They will announce an end to public service cuts (at least for a year), sell off RBS and give out a few sweeteners in the form of tax cuts. The re-election narrative will be something like this; Labour crashed the economy, we came in took some tough decisions to stabilise the economy and provide tax cuts for families. It may be cynical, that does not mean it can't work.

On the other hand if the AV referendum produces a yes vote then the Lib Dems will be emboldened. They will demand more from the government, this will inevitably annoy the Tory right, the group who really control the destiny of the coalition. The most likely scenario for an early election would be if the Tory right reacted to a yes vote by forcing an early election (which they have threatened).

Why a yes vote will damage the coalition

A yes would also embolden the opposition. Despite Labour Party members and MPs being split down the middle on AV the Labour Party manifesto in 2010 implied support for it as a voting system. Ed Miliband has joined the cross party Yes campaign and has stood on a platform with Greens and Lib Dems.

A yes vote would be a shot in the arm for Ed Miliband at the expense of Cameron. Ed Miliband could rightly begin to claim that he represents new politics, a invaluable asset after 13 years of government in the not so distant past. Good council election results and a yes vote would be an energising start for the battles ahead including over the NHS.

Cameron has already shown that he is willing to perform U-turns when middle England turn against him; forestry sell offs, Bookstart, school sports, the list is growing.

To get re-elected under the alternative vote each candidate will need at least 50 per cent of the vote. Those 172 safe Conservative seats and 29 Lib Dem safe seats will no longer be so safe. It is not difficult to see how this would make life more difficult for those government MPs voting for huge public spending cuts.

This can only lead to pressure to curb the more controversial elements of government policy. Government MPs will be more nervous about their re-election under AV and they will be less cavalier about forcing through major public service reforms knowing they need 50 per cent of their constituents to vote for them. Expect more U-turns under AV.

In short, voters who would like to see the policies of the Coalition frustrated would be wise to vote 'Yes' in the referendum. Much of the Coalition's programme, including the deep marketisation of the NHS, were not voted for by anyone in the last election, even if they seem planned.  So it is not necessarily perverse for those who see only a marginal difference between the actual voting systems on offer in the referendum to take the opportunuty to "answer a different question" as Peter Kellner's recent YouGov blog post put it. For the reasons set out above, a 'Yes' will isolate Cameron, who is more vulnerable than he appears and divide the Tories. At the same it will also open up the main division within the Lib Dems by strengthening social liberals like Vince Cable who as the Guardian reports wish to reopen the option of support for a future Labour government (and this could be decisive in future elections, whatever the referendum result). On the other hand a 'No' vote will strengthen Cameron's grip over his own party while such a defeat will lock the Lib Dems into the Coalition and its bet, which may well prove a shrewd one, that they can engineer growth in 2014 and win a second, joint term in a year later.