There are two-and-a-half interacting quirks to the British political system's psychology (though I’m sure they’re not unique to us).
First, we think as though we vote for parties when we actually elect individuals. This means that the quality of the candidates has fairly little bearing on how people vote. Every party has known times when their brilliant candidate has been crushed by a donkey with the right colour rosette. Party is the biggest factor in the polling booth, except in a few cases such as Martin Bell (Tatton, 1997) or Ken Livingstone (London, 2000). And of course a good/bad candidate can make the difference in a close race.
It also means that when MPs defect to a different party, there’s always a clamour (ritual but nonetheless sincere) for them to stand down and fight a byelection – more so than when they change any number of policy positions.
Second, we think as though we vote for a government when we actually elect a parliament. This leads to a double standard whereby manifestos are treated very differently post-election depending on which party forms the government. If the governing party drops some of its manifesto commitments, there are shrieks about ‘broken promises’. But if the main opposition party drops some of its commitments, nobody really cares (except for people in that party who liked the old policies and the various media and political opponents who enjoy mocking ‘U-turns’).
It’s broadly accepted that a party not in government has the perfect right to rethink its ideas: ‘the party lost the election’ – even though every opposition MP won their election, and did so on that set of manifesto pledges. Nobody seems to take the view that a party’s MPs have been elected to promote particular policies, regardless of whether they have a parliamentary majority or not.
(A partial qualification for minor parties: nobody votes Lib Dem expecting them to have a majority or even be in second place, so there may be more of a view among Lib Dem voters that they are electing a parliamentary pressure group to take certain positions.)
This is probably due to the facts that the composition of parliament determines the identity of the government and that hung parliaments are so very rare.
If the legislature and the executive were elected separately, no doubt the legislators of all parties would be held more tightly to their election positions. If hung parliaments were the norm, then inter-party negotiations would make it far clearer that the government derives from parliament. It would also be more accepted that no party could implement their manifesto in full, and so all parties would be equally expected to manoeuvre to advance their agendas.
The remaining half-oddity is that while we think of parties over individuals and governments over parliaments, one of the major factors in choosing which party to vote for is the identity of its leader. Brown vs Cameron vs Campbell, or Blair vs Howard vs Kennedy, is certainly much more important than comparisons of the manifesto details.
This means that when a governing party (although, again, not an opposition party) changes its leader mid-parliament, there are demands for a new election – more so than when the government drops a manifesto pledge or when the prime minister stays in place but reshuffles the Cabinet hugely.
(This is only half-peculiar, as constitutionally the identity of the government does derive from the identity of the leader of the majority party.)
The effect of all this is that we often think as though we’ve got an executive-focused electoral system in which the Commons is largely a device for annoying the government and reminding the opposition of the last election result. This goes well beyond whether a given prime minister has a ‘presidential’ style and how ruthless the whips are.