The two party system worked, just about, in the 1950s, but it doesn't any more. It has become normal for two MPs out of every three to lack the support of a majority of local voters, and an increasing number now win their seat with around 40 per cent of the vote.
The voting system used in our General Elections; First Past the Post (FPTP), meant that two thirds of MPs (433, 66.6%) elected in 2010 did not have the support of a majority of voters. Our current parliament was elected with the lowest vote share of any parliament since at least the 1920s. Things need to change.