If the candidate that the voter chooses is not elected then they are not represented.
The British system has depended on the idea that voters decide on either the Conservative or the Labour party to form a government overall and so if a voter is not represented in their constituency then at least they are nationally and, if the two parties alternate, in power a voter will have the government that they want at some stage.
This becomes more difficult in a multiparty system, so that minorities may be poorly represented, and where the electoral system produces a government that is elected with well under 50% of the votes.
Voters have to choose a representative who stands for a whole range of policies, some of which the voter will agree with and some which they do not, e.g. they may agree with the Conservative policy on taxation but not on Europe.
This becomes even more of a problem if their chosen party has to go into a Coalition to run the Government so that even more policies that the voter disagrees with are carried out. Some of the views that a voter has may not be represented by any party.
Decisions end up being taken in Westminster and Whitehall over which the voters has almost no knowledge, for example agricultural subsidy or house-building targets. These may represent the preferences of the MP rather than those of the voter.
Special interest groups can easily influence the representative without the knowledge of the voter. There is little accountability of the MP to the voter between elections.
MPs may take short-term decisions based on what they think the voters want, especially just before an election. They may support extra expenditure when this will create long-term financial problems.
The system depends on the MP being honest and hard-working. Corruption is possible as the abuse of parliamentary expenses scandal showed.
