When voters in UK general elections feel that their first-choice vote will be wasted because it is for a party that has no chance of winning, they may change their vote to their second choice
Tactical voting
Voters go against their usual instincts and vote for a candidate from a party that has the best chance of beating the candidate they most dislike
Tactical voting
Supporters of the Green Party may vote Labour to prevent a Conservative candidate from winning
A UKIP or Brexit Party voter may vote Conservative to keep Labour from winning
