I suppose it is inevitable when you are involved in a political campaign that military analogies come to mind. As a Quaker, I sometimes find this troubling, but on the other hand I think democratic politics is an alternative to war and so perhaps it is quite appropriate.

I now see Ed Miliband as a general surveying a battlefield on which he has been defeated the previous day. His decision to resign instantly following the announcement of the result is being interpreted as indicating his nobility, but accepting that Labour was roundly defeated on Thursday is just another example of how Labour has accepted the narrative of its opponents. Of all the mistakes it has made over the past year this is the most serious.

So can we consider the general election in 2015 a stunning victory for David Cameron? With only a 0.8 per cent increase in his vote share I would suggest not. It is, however, a stunning victory for Lynton Crosby. I wonder how many of us who are actively engaged in politics are kicking ourselves that we simply did not understand how he was controlling the campaign. In contrast to Labour spin doctors, Crosby has played a poor hand brilliantly. So what techniques did he use?

First, he has focused media attention on the aspect of politics they understand best: the messages. We have heard a lot about dogwhistle politics and whether the Tories were being too nasty in their messaging. We have had lengthy debates about whether it was fair to criticise Miliband for having problems eating a bacon sandwich. This was a classic example of smoke and mirrors. Because while the media were focused on these trivia, the Tories were focused on the marginal seats they needed to win to gain a majority.

They have ruthlessly targeted their coalition partners and converted their seats into Tory seats, especially in the South West, which I represent. Politics is always about majorities and it therefore comes down to numbers rather than messages. It is a failing of political commentators in this election that they were successfully diverted from this reality.

Crosby's second achievement was to create a false understanding of who was actually winning the campaign. We will wait to see why the polls were so inaccurate, and no doubt "ashamed" Tory voters were one element of this, but the complacent understanding of the anti-Tory majority that we were safe is one of the greatest explanations for the Conservative majority. Did Labour strategists believe this spin? I am sad to say that I think they probably did.

The third brilliant achievement of the Tory campaign was the way it dealt with the parties that would never hold a majority. In the case of my own party, it was clearly at Crosby's behest that Cameron made much of the need to include the Greens. This was a fairly obvious ruse to take votes from Labour but it was also a concealed tactic to divide and conquer, which Labour fell for by diverting their attention into a strategy team to attack our party and a massive (and gloriously unsuccessful) campaign to unseat Caroline Lucas in Brighton. We felt at the time, and more so now, that they should have been focusing their attention on more important enemies.

As I survey the battlefield I can see a PowerPoint slide with three points on it: marginals, minor parties and narrative. These three points explain how a tiny increase in vote share for the Conservatives has been turned into a massive shift in power whose economic, social and environmental consequences will be devastating. For the past year Crosby has played our politicians and, more importantly, our journalists, who willingly trotted out his narrative and implemented his campaign for him.

It seems so inglorious to win an election in this way that I am left wondering how much of the strategy is clever and how much is unacceptably deceitful. Why does this election result feel so unfair? The answer is that the whole Crosby strategy works around an anachronistic voting system. He is not to blame for that, and he has exploited it in a way that can only reinforce his reputation. Our problem now is that the system he used so effectively has handed absolute power to the very people who have the least incentive to change it.

Sometimes we comfort ourselves by thinking that nobody actually dies in the political struggle. Sadly this is not the case. Five years of Tory government could mean deaths from air pollution, deaths of old people in poorly insulated under-heated homes, deaths of disabled people who will not be properly looked after, death by suicide of those whose jobs are simply too inhumane to be tolerated. As politicians we should never forget these human casualties. But our priority should be to reject the divide-and-rule strategy of the Tories and to work together against the voting system that has just given all the power to a party only a minority support.

Molly Scott Cato is Green MEP for South West England