By Jenny Matthews
Tactical voting - when people vote not for the party they really like, but for another in order to keep out a more disliked rival - played a role in the 1997 and 2001 polls.
But what about this time around? Who would benefit most from it - and what are the risks?
There is a strong interest among voters in tactical voting for the 5 May election, if the number of websites devoted to it is anything to go by.
The sarcastically-titled site Backing Blair informs "disenfranchised Labour voters" how to punish the prime minister.
Singer and campaigner Billy Bragg is encouraging Dorset residents to vote tactically
"After a lot of people get over the initial prospect of voting Tory, the level of support has been really quite good," Tim Ireland, the man behind the site, told BBC News.
"We're doing it on a constituency by constituency basis, you go to the website and you enter your postcode and you are given advice as to the what the most viable candidate against any given Labour candidate is."
Another site, Howard's End, is offering vote-swapping opportunities - where, for instance, a Lib Dem supporter in a Conservative-held seat which Labour could win, uses the internet to find a Labour supporter in a Conservative-held seat where the Lib Dems could win - and make a pact to "swap" votes.
Left-wing rock singer and campaigner Billy Bragg is also resurrecting his 2001 vote-swapping website in what he says is a bid to stop the Conservatives becoming "resurgent".
At least one Labour party member, David Finnitch, 70, from Folkestone, has been won over to the idea of tactical voting, because he says there is "no chance" of the party winning in his constituency - so he may as well try to get the sitting MP, Tory leader Michael Howard, out instead.
"If the majority of Labour voters would pull over, and top up with the Lib Dems, we can move Michael Howard out of this area, I'm convinced of that," he told BBC News.
But constituency party chair Christine Walters sums up the feelings of many when she says she would feel she had betrayed the party if she voted for anyone else.
"I'm not quite sure how I'd manage it really, I'd probably come out and slash my wrists," she said.
Bragg claims some success in the 2001 election with his vote-swapping campaign to keep the Conservatives out in Dorset South and Dorset West, even though they held on to Dorset West.
He is again urging voters to vote tactically this year to stop the Conservatives - pushing them into second or third place where possible. His vote-swapping website is due to be up and running in the next few days.
He agrees with Ms Walters that tactical voting involves some "hard choices".
But those who profoundly disagree with Labour's actions in government and want to punish them should be careful, he warns.
"'Punishing' Labour with your vote is a dangerous game to play. This is an election of outcomes, not a referendum on the Iraq war," he said.
"The last thing we want is a resurgent Tory party which forces Labour to tack to the right in the direction of their main perceived threat."
The Conservatives are certainly hoping to take back many of the seats they lost to tactical voting in 1997 and 2001, reckoning that many Lib Dem supporters will have been alienated from Labour by the Iraq war.
It is one of the factors - along with their poll lead among people likely to vote - the Tories believe could lead to a much stronger showing on 5 May than the opinion polls would suggest.
A Conservative spokesman said: "There was a certain degree of 'tactical unwind' evident in the European elections last year, particularly around the West Country and the Midlands."
He said people who "had voted for different parties to get rid of the Conservatives in 1997" were now returning to their "normal" voting preferences.
Of course, the main parties do not officially endorse tactical voting - even a Liberal Democrat spokesman, who admitted they were often the "happy recipients" of tactical votes, said he would like supporters simply to "vote for us".
A Labour spokesman said: "We want people to support the party."
Is it possible to send a complex message with your ballot paper?
Musician and record producer Brian Eno has a similar view to Billy Bragg on the outcome he wants to achieve - but a different way of going about it.
He wants people across the nation to vote Lib Dem in what is essentially a "large-scale tactical vote".
"There's almost no chance that Labour will lose this election, there's almost no chance the Conservatives will win it, so the interesting question is, who do you vote as the opposition?" he said.
"A vote for the Lib Dems could move the whole political process somewhat left-wards."
But Guardian columnist Jonathan Friedland, who favours Labour, agrees with Bragg that tactical voting is a "blunt instrument" which can do more damage to any one party than those wielding it intend.
Many voters, he argued, wanted the outcome that "Labour wins, but Blair's taken down a peg or two".
"Or we still get a Labour government for domestic things, because that's what we like, but they learn their lessons over Iraq. Now that is a very complex proposition which is not written anywhere on the ballot paper."
John Curtice, professor of politics at Strathclyde University, said tactical voting played an "important" role in the last two elections.
Typically, it involved natural Lib Dem or Labour voters switching to the other party to keep the Conservatives out.
In 2001 particularly, "Liberal Democrats switched to the Labour Party in quite substantial numbers," he said.
"[There were] 3%, 4%, 5% of Liberal Democrat voters evidently switching to Labour, and thereby enabling them to pick up seats they otherwise would not have done."
This time around, however, that is unlikely to be the case, he believes.
"The crucial thing about this election is not whether we're going to get more tactical voting, but whether we're going to get less of it.
"Polling evidence is beginning to mount up that Lib Dem supporters no longer have the kind of attitudes that are going to encourage them to vote tactically.
"People who vote tactically are those who like both the Liberal Democrats and Labour and hate the Conservatives. There were lots of those in 1997 and 2001 - the polling evidence is that there are far fewer of them now," he said.