Why what has happened in Greece couldn't happen here

Two-party politics (let alone three or more party politics) will only be dead if our electoral system changes. I have defined four main streams in English politics: 

• Green/Socialist 20% 
• Social Democrat 30% 
• One Nation Tories 30% 
• Independent Right 20% 

You can quibble about the percentages I suggest but if you ignore current Party affiliations surely the streams are clear? With a more proportional voting system coalitions of Right or Left would be likely (though a Grand Coalition of the centre, as in Germany, could not be ruled out). 

The third party in England after the Election, as now, will be the LibDems. Despite their lowly position in the polls the strength of incumbents in many constituencies will give them perhaps 30 seats. And yet they do not represent any of the political streams I identify! If the Party didn't exist it's members would scatter to the Greens, Labour and the Conservatives (Orange book neo-liberals). There is no coherent logic to the LibDems at all. And for them rather than the Greens or UKIP (both of which could out-poll them nationally) to be the third player in a coalition is hardly very democratic! The other effect of FPTP is that politicians stay within the two main parties rather than going to their natural home. There are plenty of Tories who despise "One Nation" Cameron but don't follow this through by defecting to UKIP. There are plenty of Labour members who would be happier in a Green/Socislist party which more strongly reflected their views.

Across Europe the four political streams I describe also exist but in many countries they have a seat allocation matching their vote allocation, This has allowed the Greek equivalent of the Green/Socialist stream to gain power. In Britain FPTP has prevented three party politics from truly arriving and 3+ party politics won't arrive this year either - in seats that is. UKIP and the Greens do represent coherent streams in British politics. But FPTP means they are unlikely to be any sort of player this year. Odd sort of democracy !