The way I see it, voting for UKIP IS a tactical vote.
Sure, it might be handing Labour a victory this time round, but if UKIP's percentage of the votes is high enough, it will send a loud and clear message to the Conservatives.... that if they ever want to get elected again, they must give people the opportunity to decide whether they want to be In / Out of that "ever closer union" that is now looking very different from the EEC voted for in the 1970's.
If we claim to be a democracy, then really, it's only reasonable that the people should at least be asked! (Of course, technically we're a monarchy so the only opinion that actually matters is that of the Queen!)
That I see constant headlines on the BBC or The Telegraph suggesting that if people vote UKIP the UK will sink into the ocean after the sky has collapsed, and that millions of jobs will vanish into the ether, suggests that certain political groups (and their media / economic backers) are actually a little scared
Sorry, but if you vote for Labour or the Conservatives, you're essentially endorsing the status quo.
If you vote UKIP, you're at least saying to the two main parties, "Do something about this, or else."
Yes, it may be a protest vote for many... but if enough people protest "loudly" enough, things MIGHT change. If nobody protests, nothing changes.