Hypothetical situation (on which someone with experience of tactical voting may wish to shed some light).
You live in constituency S. There are 5 candidates in upcoming general election (candidates AA, BB, CC, DD & EE). They represent parties V, W, X, Y & Z.
The constituency you live in is currently represented by AA (of party V) whose party are currently the governing party but who look like they are going to lose the coming election. While AA is a member of the governing party, they have shown themselves to be somewhat independent-minded and occasionally voted with their conscience. You don't have a problem with them at all, but don't particularly like the party they represent.
Candidate BB's party W were 2nd in the constituency last time out, and have constantly told you that "only they can win here", despite the last 2 elections in the constituency pushing the party's vote down in the area. You are not keen on these kind of games, don't like that tactic and are generally underwhelmed by the party.
Candidate CC's party X finished 4th here in the last UK election but have proved stronger across Scotland. They have performed creditably in government and look like a party on the up. You strongly support the party's goals but have a particular dislike for their chosen candidate.
Candidate DD's Y party look likely to be the next UK government, but remain a way off winning this seat. While you recognise the strength of some of their arguments (and the charisma of their leader) you are loathe to support them and a local candidate who also rubs you up the wrong way.
Finally, candidate EE's party Z look like facing a struggle to return their deposit, though they showed fairly strongly in the previous (European) election in the area. You appreciate the party's intentions - and have voted for them in the past - but you recognise the difficulties facing them in what is not a PR election and feel that voting for them this time may be a wasted vote.
So, here's your choice reader. Do you:
A) Appreciate the work of your current MP (of party V) and, in your concern that the constituency may be represented by the wishy-washy party (W), lend your support to the incumbent.
B) Vote for the wishy-washy (W) party in the hope that your vote is enough to win the seat for them over the incumbent.
C) Go with the party you strongly support (X) and ignore your feelings about their candidate (increasing their share of the national vote by a minor percentage).
D) Recognise that there is a bigger picture, become a glory-hunter and vote for party Y who won't win this seat but will probably win the election - giving you the opportunity of telling people that yes, you voted in the government.
E) Ignore the fact that your second choice party (Z) have little chance of winning the seat and try to help them secure their deposit.
F) Stay at home on election day.
So there you are reader. The choice, as they say, is yours. Answers on a postcard (or in the comments).