By Nick Assinder
Political Correspondent, BBC News website
It is the political sin everyone indulges in but nobody wants to admit to.
And it looks like it is about to escalate in the closing days of the current election contest.
Tory campaign targets Blair
Negative campaigning, what else, has been a feature of virtually every election in recent memory.
It is just that those accused of indulging in it claim they are up to something quite different, usually "telling it like it is", as Michael Howard currently insists.
His determination to "tell it like it is" has now seen the 2005 campaign taken to a new, personalised level with allegations Tony Blair is a liar top of the Tory agenda.
Meanwhile, neither Tony Blair or Liberal Democrat leader Charles Kennedy hold back on the rhetoric when giving big speeches at election rallies.
Labour got into trouble over personalised posters featuring Michael Howard at the start of the campaign.
And the Lib Dems' most recent recruit, ex Labour MP Brian Sedgemore, has accused Mr Blair of telling "stomach turning lies".
But while many may well believe such campaigning is not nice, and claim it turns them off, the truth is it often works, particularly when it comes to hand-to-hand fighting over the most closely contested seats.
And, as many have been predicting from the start of this contest, that is exactly what the campaign has come down to - a virtual seat-by-seat fight in marginals where, as the prime minister has himself admitted, just a few hundred votes can swing it.
Labour's campaigns chief, Alan Milburn spelled it out when reacting to recent polls suggesting that, amongst those certain to vote, Labour and the Tories are neck and neck.
Controversial Labour poster
"The worry for us is that the propensity to vote amongst Conservative voters seems to be higher than the propensity to vote amongst Labour voters. That plays very much to the Conservative strategy".
His comments may appear dangerously candid. In fact they are designed to warn Labour waverers they risk letting in the Tories through the back door.
Similarly, Mr Howard's apparent confession he is running second is designed to shore up his core vote while encouraging those Labour waverers to believe they can afford a protest vote against Tony Blair.
And, despite the claimed distaste for negative campaigning, they have all been at it one time or another.
In 1983 and 1987, then Labour leader Neil Kinnock was subjected to a highly negative campaign, much of it centred on his personality.
In 1997, Labour focused much of its campaign on Tory sleaze and the personal behaviour of MPs.
And looking beyond the UK to the US, from where campaign lessons and tricks are often imported, the two most recent presidential campaigns have been marked by personal, negative attacks.
Milburn looked to marginal seats
It is also suggested by Labour that the Tory strategy has been imported to Britain by the party's Australian campaigns chief Lynton Crosby, who pulled off a sensational victory for a different Mr Howard there with a similar campaign.
So, as we enter the last lap of this contest, all three parties are honing their messages.
Labour believe it can focus attention onto the "stark choice" between its record on the economy and public services and a dangerously opportunistic Tory party lacking credible policies.
The Liberal Democrats will seek to rise above the negativity, claim the Tories cannot win and encourage voters to pitch for their "real alternative".
And the Tories will bring it down to a matter of honesty and trustworthiness and an appeal to voters to "send a message" to Tony Blair.