In ordinary circumstances votes, like wives, are not casually swapped around. But that appears to be changing in 2015, as a group of determinedly anti-Tory activists encourage left-leaning types to switch sides.
The basic idea behind VoteSwap relies on the old principle of tactical voting: that voters could be persuaded to choose a party other than the one they support in order to stop their political enemy from winning.
Normally this is a straightforward, somewhat grubby process. It is not especially healthy. It is a perversion of the democratic system. But it has the promise of being effective in preventing the hated alternative from triumphing. In Scotland, such is the enmity provoked by the SNP surge that unionists are fostering a frenzy of tactical voting ahead of May 7th.
The prospects in England are more limited. But on the left of British politics the enemy is clear enough.
Stopping David Cameron from spending the coming years in No 10 via tactical voting is a tough ask, though. As a general rule, the best way of thwarting the Tories is to back Labour. There aren't many alternatives. The Liberal Democrats have to be discounted completely because of their habit of actively propping up Conservative ministers.
That just leaves the Greens. Together with Labour, VoteSwap explains, lefties are faced with two parties with different policies which, it concedes, stand against each other. "But many of their voters share similar values. And if they have one thing in common it is not wanting to wake up after the election to a Conservative prime minister."
By entering your postcode into the website - or you can search by constituency if you prefer - site users are offered a bit of handy advice about the best way to cast their vote. This doesn't always result in a tactical voting suggestion, mind. Take Ashfield, where Gloria de Piero has a 0.4% majority. "This is not a seat where we would advocate a vote swap," the website advises. "While we expect Labour to win this seat, the party's relatively small majority at the last election means Labour supporters will be reluctant to swap their votes here. We therefore advise Green and Labour supporters to vote according to their preference."
Swapping votes also isn't a good idea in Norwich South, which is a target seat for both the Greens and Labour. Again, the instruction is to "vote according to your preference".
But it's a different story in constituencies like Worcester, where Tory Robin Walker is defending a 6.1% majority. Here Green supporters are urged to vote Labour "in order to stop a Tory government". Why? "Labour has a reasonable chance of winning this seat. We suggest you vote Labour here and if you are a Green supporter swap your vote with a Labour supporter willing to vote Green elsewhere."
The big innovation here is the idea of an informal 'swapping' of a vote. Doing so would, in theory, result in the efficacy of both votes being significantly increased. They might actually make a difference. And swapping votes soothes the conscience of those who might feel that they're betraying the party they really support.
Unlike in Scotland, where tactical voting organisations like Scotland's Big Voice retain strict anonymity, VoteSwap's creators are happy to be named. "We're a bunch of people who all are progressive campaigners working for various different organisations, but have had different conversations about this, and all doing this in a volunteer capacity," says co-founder Huw Jordan. "Some of us are Labour supporters in the past, some are agnostic about party politics, some are Green, but we all know we don't want a Conservative government. We asked ourselves, how do we break down this barrier and stop this from happening?"
But what about the poor old Labour and Green candidates, slaving away on the doorstep to maximise their vote? Their efforts are being severely undercut by this website. Many would view it as nothing less than a betrayal.
"For a lot of those Labour and Green candidates, the vote won't make a difference to the result of the election," Jordan adds. "We are being very pragmatic about this. We want a particular result and we know a lot of Labour and Green supporters want that result - we don't want the further cuts and further privatisation of another Conservative government. We're being very pragmatic and tactical about that. If we had a PR system, it would be a completely different matter, those candidates might not be so annoyed. We're aware this site might be slightly provocative but we think it's justified in the context of the voting system."
A lot of the provocativeness only really emerges when you consider its prospects for Green candidates. Take its advice for Brighton Pavilion, where the Greens' only MP in the last parliament, Caroline Lucas, is defending her seat. As in Norwich South, VoteSwap says: "This is not a seat where we would advocate a vote swap". That's because this is a Labour target seat as much as it is a Green one. It's hard to avoid the conclusion this is a website that helps Labour.
What an excellent idea. A website that allows you to swap votes to keep out the Tories, or PR beneath the radar. http://t.co/GaGglrWn8v— Iain MacDonald (@frugalmac50) April 10, 2015
The Greens, which are being squeezed up and down the country, are certainly doing their bit against tactical voting. The party is full of anti-tactical rhetoric on social media. They take the view that - shock, horror - you should vote for the party whose beliefs you actually, um, support.
"I'll not be voting Green to keep the Tories, or the Lib Dems, or Labour out of government – that's not the point of voting," writes one Green supporter. "I'll not be voting Green because they're the least worst of the options, but because in my opinion they're by far the best option. There's absolutely no way my voice could get confused with any other voice. I want Green policies enacted, so I'll vote for them."
And then there's the Green candidate who's put that message into a more lyrical format. If small parties continue to struggle, Theo Simon warns, "we will remain prisoners of this two-party system potentially forever".
But in Simon's seat, Somerton and Frome, VoteSwap is on his side. "Labour has little chance of winning this seat," it states. "Greens can happily vote Green here and if you are a Labour supporter you should swap your vote with a Green supporter willing to vote Labour in a target seat."
If everyone followed VoteSwap's advice, the result would be a significantly increased national vote share for Natalie Bennett's party - but more MPs, in all probability, for Labour. Some Green politicians might accept that, but it hardly turns the system to their advantage. Others will see VoteSwap for what it is: a brazen attempt to get their votes.
It leaves Green supporters facing a tough choice. If they really want to stop the Tories, abandoning their own party is the price they must be prepared to pay.