A. W. Young Liberal William Baliol Brett Conservative A by-election was held on 1 May 1866 to return an MP for the constituency of Helston, England.

Two candidates contested the election: Robert Campbell for the Liberal Party and William Baliol Brett for the Conservatives.

[1] In the immediate aftermath, a report in the Royal Cornwall Gazette said that the result had been a surprise, and alleged that "certain measures ... were adopted to induce men to break their solemn pledges".

[3][4][5] In February 1866, a petition was presented to Parliament by three Helston constituents, accusing Young of "acts of bribery and corruption" during the election.

[6] At the subsequent hearing in April, Mr W. H. Cooke—counsel for the petitioners—announced that Young had accepted that without his knowledge, some of his representatives had been guilty of bribery, and he would not contest the charge.

[8] The Liberal Party put forward Robert Campbell, who had previously served as High Sheriff of Berkshire, while the Conservatives were represented by William Baliol Brett, a Queen's Counsel on the Northern Circuit.

In a letter published in The West Briton & Cornwall Advertiser, Campbell said his "political opinions are in the main identical" to Young's.

The Liberals complained that at 3:56 pm a voter, Martin, had been prevented from casting a vote for their candidate by the Conservatives "taking possession" of the hall.

The Reverend Isaac Rogers gave evidence that he had voted, despite no longer residing in the house he had previously occupied in the constituency, in the belief he was still eligible to do so.