Conservative leader Michael Howard has accused Tony Blair of trying to pull off a "con trick" over tax rises for the third election running.
Tony Blair wanted to talk about education, not himself
The campaign is becoming increasingly personalised after a Tory poster accused the Labour leader of lying.
Tony Blair said he did not care about personal abuse as he launched a fierce attack on the Conservative education policies, calling them "extreme".
Charles Kennedy says the Lib Dem mood is best since the "heady days" of 1983.
He said the Tories' tactics showed they thought they would lose the election.
"They are falling back now on the most negative form of personalised campaigning," said Mr Kennedy.
"It won't do them any good, it won't do the quality of the general election campaign any good."
The latest Tory poster says: "If he's prepared to lie to take us to war, he's prepared to lie to win an election."
Speaking in Edinburgh, Mr Howard attacked Mr Blair for delivering a "stab in the back" to the Scottish infantry regiments facing merger or disbandment.
Pointing to "tests of character", Mr Blair had twice raised taxes after elections and was refusing to admit he would need to do the same again.
"He has got away with it twice before and thinks he can pull off this con trick a third time," said Mr Howard.
"But what does he take Scottish voters for: does he think they are idiots?"
Asked if he had ever lied in the past, Mr Howard said: "I'm not aware of any occasion when I have deliberately or knowingly misled people and that is the charge I lay against Mr Blair."
'Back door plan'
Labour says it will not be drawn on the personalised Tory attacks but its latest posters accuse Mr Howard of having a "hidden agenda" for NHS charges.
The message will be underlined in a Labour election broadcast on Wednesday.
Meanwhile, chancellor Gordon Brown has defended Tony Blair's decision to go to war in Iraq.
Mr Blair used a speech at a school in Bolton to renew his attack on the Tories' pupil passports scheme and to talk up Labour investment plans for pupils and school buildings.
The Conservatives had raised immigration "in a profoundly unpleasant way", he said.
"Let the Tories keep up their personal attacks on me," he said. "I will keep setting out the policy choices that matter to the British people.
"Let them go negative, negative, negative. I will stay focused on education, education, education - yesterday, today and tomorrow."
The Conservatives plan to let parents spend the value of what would be spent on a state education - £5,500 per pupil by 2008 - on a private education for their child.
The schools would not be allowed to charge any fee on top and the Tories say the scheme would improve choice.
Mr Blair claimed the policy would take about £2bn out of the state school system and said Tory plans to allow all schools to choose pupils by ability were "deeply unfair".
There was much more to be done, said Mr Blair, arguing school discipline, another key Tory campaign theme, was vital.
He also said the Lib Dems were "peddling a delusion" because their spending plans did not add up.
The Lib Dem highlighted their guarantee that in the core subjects of English, maths, science, modern languages and computing pupils would be taught by teachers who are qualified in those subjects.
Mr Kennedy said: "Enthusiasm. Dedication. Optimism. Expertise. These are the qualities of our best teachers and I want the whole profession to be equipped with the skills and support they need to do the job."
The party would fund its plans for smaller class sizes by scrapping the Child Trust Fund.
A new Mori poll for the Financial Times of people certain to vote suggests Labour's lead has narrowed, with the party on 36%, the Conservatives on 34%, up 2%, and the Lib Dems on 23% , up 2%.
But the Conservative campaign has been criticised by former party chairman Norman Tebbit, who described it as "bits and pieces without a really strong theme".