The outcome of an election may be questioned in a special electoral court by the presentation of a petition under the Representation of the People Act.
Just one voter, or an unsuccessful candidate, can take advantage of this mechanism in the case of disputed parliamentary elections and elections to the European Parliament - upon payment of certain fees.
For local elections, the petition needs to be presented by 4 or more voters or an unsuccessful candidate.
One of the best publicised cases occurred in 1961.
Tony Benn was disqualified from taking his seat in the Commons after he inherited a peerage and became Viscount Stansgate.
Mr Benn won the ensuing by-election, yet was still ruled to be ineligible to sit in the Commons by an electoral court after his opponent, Malcolm St. Clair, appealed against the result.
A recent example of an electoral petition causing upheaval is that of Gerry Malone in 1997.
On 6 October 1997 the High Court declared the election result in Winchester void.
Former Conservative Health Minister Gerry Malone had lodged a petition after losing the seat to Liberal Democrat Mark Oaten by two votes.
55 ballot papers were rejected by the Returning Officer as they had not been stamped properly by polling station staff.
Lord Justice Brooke ruled that the fact that these papers had not been stamped rendered the result invalid.
In fact this petition did not help Mr Malone in the long run. Mr Oaten remained as MP until the re-run election, at which Gerry Malone lost again.
In the more distant past, bribery, multiple voting, undue or false election expenses and misrepresentation have been common reasons for parliamentary election results to be challenged.