1866 Helston by-election

A by-election was held on 1 May 1866 to return an MP for the constituency of Helston, England. The by-election was caused by the declaration that Adolphus Young's election in the 1865 United Kingdom general election was null and void due to bribery. Two candidates contested the election: Robert Campbell for the Liberal Party and William Baliol Brett for the Conservatives. On the original count, both candidates received 153 votes but Campbell was declared the winner after Thomas Rogers—the mayor of Helston, who was serving as the returning officer—made a casting vote in his favour.

The decision was appealed, and upon scrutiny, Brett was declared the winner after it was found that Campbell had received a vote from a local clergyman who did not have the right to vote due to a lack of residency. This election led to Parliament deciding that in future, if an equal number of votes were recorded for two or more candidates at an election, all such candidates should be elected.