Economist articles putting the party system and FPTP in historical perspective.
FPTP looks set to benefit SNP, and squeeze out Green and UKIP. Worries about "instability and a crisis of legitimacy"!
http://www.economist.com/news/leaders/21644147-britains-slide-six-party-politics-presages-instability-and-crisis-legitimacy-great
The second one has a chart showing proportions of votes for the parties every year from 1885 when FPTP was introduced.
http://www.economist.com/news/briefing/21644142-two-party-political-system-under-unprecedented-pressure-breaking-point