Stephen Tall: Do you want to be in power? The new politics demands a Tory alliance with UKIP or the Lib Dems

Stephen Tall is the Co-Editor of LibDem Voice. Follow Stephen on Twitter.

British politics used to be pretty clear-cut. 'Every boy and every gal / That's born into the world alive / Is either a little Labour/ Or else a little Conservative!', to update WS Gilbert's famous ditty for the post-war era. In 1951, in the last great electoral contest between Churchill and Attlee, 97% of voters opted for one or t'other on a turnout of 83%.

That duopoly crumbled over the next half century, like the dry mortar of a once grand castle. At the last election, just 65% of voters picked either of Messrs Brown or Cameron on a turnout also of 65%. For a while it looked like 2010 might mark the nadir of 'Labservative' fortunes, with the Lib Dems now in government facing a vicious squeeze. The 2011 local elections saw a slight revival in two-party fortunes, to 72%. It looked like they could relax and confidently await the return of business-as-usual.

But it's not quite worked out like that. In the 2012 elections, their combined total dipped to 69%. And then came the Ukip surge. Labour and the Conservatives slumped to a paltry 54% joint share on 2nd May 2013, an historic low. The two-party grip has been fractured for good. There are still some optimists who think the Big Two can turn the clock back to those good old days of the 1950s, and re-capture the binary certainties of 'Clem v Winnie'. They are, I think, on the wrong side of history. Voters are getting more choosy, not less; becoming less tribal, not more. You may as well try squeezing toothpaste back into the tube.

You know the old joke? 'There are only 10 types of people in the world. Those that understand binary and those that don’t.' As a Lib Dem, and therefore de facto third-party fanboy, I've often criticised the media obsession of seeing all issues through a binary lens. Most people's views are more complex than the over-simplicity of 'right' and 'left'. The lefty who thinks Michael Gove's got a point. The conservative who supports EU membership. The liberal who backs Trident. They all exist, they're all real people. But they can't be neatly divvied-up, like sheep and goats, into left and right.

Yet deny it as I might, there is an essential truth underlying binaries: that people can be divided into different and opposite world-views. The best definition of what these are was offered by this site's former owner, YouGov pollster Stephan Shakespeare, in 2005:

We are either 'drawbridge up' or 'drawbridge down'. Are you someone who feels your life is being encroached upon by criminals, gypsies, spongers, asylum seekers, Brussels bureaucrats? Do you think the bad things will all go away if we lock the doors? Or do you think it's a big beautiful world out there, full of good people, if only we could all open our arms and embrace each other? Depending on which side we take, we regard 'drawbridge up' people as unpleasant, or 'drawbridge down' people as foolish.

More pejoratively still, Robin Cook labelled drawbridge up people 'chauvinists' (reactionary, isolationist, anti-European, anti-immigration, anti-asylum, pro-hanging, anti-abortion, convinced ‘prison works’, little Englander, nostalgic) and drawbridge down people 'cosmopolitans' (outward-looking, internationalist, pro-European, pro-immigration, pro-asylum, anti-hanging, pro-choice, believes in rehabilitation, multi-culturalist, progressive, forward-thinking).

I was reminded of these political binaries when I saw the polling relating to the detention of David Miranda, partner of Glenn Greenwald, the Guardian journalist who broke the story of Edward Snowden's leaked revelations about the activities of the US and British intelligence services. Mr Miranda was detained under Schedule 7 of the Terrorism Act 2000, which gives the police the power to hold any citizen for up to nine hours without any need for evidence or even reasonable suspicion. It's a law with majority support across voters of all parties (tough law-and-order policies generally play well). But look at the the net figures - those who back it less those who don't - broken down by party support and you see big differences emerge. By overwhelming margins, 68% of Conservative and 61% of Ukip voters back Schedule 7; in contrast, net approval is much lower for Labour (29%) and Lib Dems (17%).

It strikes me that we're starting to see the shape of the new politics. On the one side, two 'drawbridge up' conservative parties (Conservatives and Ukip). On the other, two 'drawbridge down' progressive parties (Labour and Lib Dems). Two Party Politics is dead! Long live Two-Party Party Politics. Tribal supporters of each will hate being bracketed with the other, of course, in true Monty Python style ("'Judean People's Front'. We're the People's Front of Judea!"). But their leaders are going to have to get to grips with this new reality.

The problem is especially acute for the Tories. Because while there is probably a 'drawbridge up' conservative majority to be won in the UK, it's very unlikely that the Conservative Party can deliver such a majority on its own. Tory MPs may have enjoyed a harmonious summer love-in, but the electoral maths of their own 35% strategy (about which I wrote here some weeks ago) still points to Labour becoming the single largest party in 2015, especially with Ukip's support likely to spike again at next May's Euro and local elections. The trouble for 'drawbridge up' conservatives is that the first-past-the-post electoral system means even soaring Ukip support is very unlikely to translate into House of Commons seats for Farage & Co.

The time is coming when the Conservative Party is going to have to face an (for them) unpleasant truth: they just cannot win enough votes in the country at large to win a workable majority in Westminster (by which I mean one not reliant on Peter Bone and his fellow head-bangers).

On accepting that truth, a clear choice follows. Those Tories who want to see a drawbridge up conservative majority government should back a Conservative / Ukip alliance as the best way of achieving that. (Of course that also means supporting some form of electoral reform, but I'll leave that bit of persuasion for another day.) However, those who want to see a drawbridge down conservative majority should back a continuing coalition between the Conservatives and Lib Dems - and start preparing, as Labour has begun to do, for a second hung parliament.

That's your choice. A binary choice. Which is it to be?