Tactical voting lets you use your vote strategically to get the overall election result you want to see.
The UK uses an election system called first-past-the-post, where the candidate who gets the most votes in each constituency wins. This makes it possible for MPs to get elected without winning the support of a majority of the voters, if the opposition is divided.
By voting tactically, you can overcome this problem, uniting behind the candidate who has the best chance of defeating the Conservatives where you live. They may not be your first choice, but your vote for them can help stop the Tories. This website is a tool to help you decide on your tactical vote.