Why is the British electorate fragmenting?

The Economist, referring to “six-party politics,” reports:

In 1951 the Conservative and Labour parties together scooped 97% of the vote; in May, opinion polls suggest, they will each win barely a third.

You will note that the UK has a fairly strict “first past the post” system, so if such fragmentation happens in their system perhaps it could happen anywhere.  A second Economist article offers a few hypotheses about why this is happening:

1. People are now used to shopping in markets, and on the internet, for exactly what they want.

2. Politics has become increasingly multi-dimensional; this article cites the possibility that a “libertarian-authoritarian” axis may be replacing “left-right,” or consider the issue of Scottish independence.

3. Perhaps current politicians are less skilled than Thatcher and Blair at attracting the allegiance of a broad cross-section of British society.

I worry that the general decline of discretionary government spending may make politics less stable (but also more interesting, not necessarily in a good way).  When there is plenty of spending to bicker about, politics revolves around that question, which is relatively harmless.  When all the spending is tied up, we move closer to the battlefield of symbolic goods, bringing us back to “less stable and more interesting.”  If that is a cause, this trend is likely to spread.  (In a new paper David Schleicher argues that electoral reform may not stop polarization and splintering.)

Arguably a good deal of American politics is a cloaked debate over whether a particular kind of Christian worldview ought to enjoy higher or lower social status.  Since Britain doesn’t have much religion, perhaps that is why they are fragmenting in so many other directions.  Exactly which British debate is supposed to be imposing the uni-dimensionality on the political spectrum?