To explain what I mean by "tactical voting": imagine that you were the only voter in your constituency and therefore whichever candidate you voted for would become your MP. Which candidate would you vote for? Then think about which candidate you actually plan to vote for in real life. Are the two the same? If not, you are clearly voting tactically. It seems to me there are the following possible scenarios:
A. Yes, I'm voting tactically.
B. No, I don't need to vote tactically because the candidate I like best (a) does stand a decent chance of winning, or (b) is the candidate with the best chance of beating the person I really don't want as my MP.
C. No, I'm not voting tactically. The candidate I'm voting for stands no chance of winning, but I live in such a safe seat for one party that I might as well vote with my heart.
D. No, I'm not voting tactically. Even though it's not obvious who will win in my constituency, I am voting for a candidate who has no hope of winning. I'm doing that because as a matter of principle I want to support my preferred candidate/don't feel able to support any of the candidates who do stand a chance.
Think I've thought of all scenarios (assuming you are actually voting)! Which one are you? (I'm B.)