The link below is to a Guardian newspaper article on tactical voting and it’s worth a read:-
Because of our warped 1st Past the Post electoral system we are often placed in a situation where we have to vote for a candidate/party we don’t really support to stop a candidate/party whom we really dislike from being elected. Under a fair/proportional voting system this would not be necessary but we are where we are until we get fair votes.
There are probably two types of anti-Tory/anti-Brexit voters who are looking for advice as to how to vote so as to maximise the possibility of stopping a Tory/Brexit supporting candidate from winning in their constituency. Firstly, there’s the simple issue of trying to stop a Tory being elected and in England it will almost always be a case of voting for either the Lib Dem or Labour candidate who is more likely to beat the Tory. There will be, of course, a very small number of constituencies where the Green is more likely to beat the Tory than the Lib or Lab candidates.
For me the complication is where you want to stop a Brexiteer candidate winning in your constituency because of course there will be significant numbers of of Labour candidates who are Brexiteers.
OK, in this scenario, you know you want the Tory/Brexit Party candidate to be beaten so if there’s a Lib Dem candidate the answer is clear as the Lib Dems are openly opposed to Brexit. However, what if you are being told that the Labour candidate is best placed to beat the Tory? The answer is to try to look very carefully at the Labour candidate to see if they are/could be a Brexiteer too.
The problem here is that many Labour candidates and former Labour MP’s have kept very quiet about their Brexit views so getting to the bottom of what they think about Brexit can be hard going if not impossible. I’m guessing that central Labour advice to their candidates has been to keep quiet as there have been too many of them saying little or nothing even when asked directly! And just because your sitting Labour MP, who is trying to get re-elected at the upcoming GE, voted to Remain in the 2016 Referendum it does not necessarily mean they will stick to being a Remainer after the GE. Remember Labour Party policy is not to come down on either side of the Brexit debate before the GE and they actually want to negotiate another Brexit Deal with the EU for us to leave, if they get elected. So unless your Labour candidate is in effect breaking with Labour policy and is saying they will support Remain after the GE you could end up voting for a Labour candidate who will back Brexit!
Be warned a Labour vote could inadvertently be a vote for Brexit even if your intention is to vote Labour to stop Brexit.
And then looking at the telescope from the other end what do you do if you are faced with multiple Brexiteer candidates in your constituency and you want to stop Brexit? In this scenario the Labour, Tory, UKIP & Brexit Party candidates are all Brexiteers. The answer is of course is to vote for Lib Dem.
Oh for a fair electoral system where we could simply vote for the candidate/s we liked the most!