Speaking in Derby, he said: "They have disqualified themselves as as a serious party of government.
"They have abandoned the centre ground.
"They are camped on the Right - pointing in the direction of the past.
"And now it's too late for them to return to the mainstream."
Mr Blair continued his efforts to boost voter turnout by insisting that every single vote would count on Thursday.
He took his party's morning news conference to the seat with the smallest Labour majority, Wellingborough in Northamptonshire.
" If you want more equipment, more hospitals, then go out and vote for them "
With only two days to polling, Mr Blair said: "You, the people, are the boss... the reins of power are in your hands."
He urged people to speak out "clearly and unequivocally that no party should ever again attempt to lead this country by proposing to cut Britain's schools, hospitals and public services".
Amid talk of a possible Labour landslide, Mr Blair said:"Do not listen to anyone who tells you this election doesn't matter or that the result is a foregone conclusion."
He emphasised that with a Labour majority over the Conservatives in Wellingborough in 1997 of just 187, every vote counted.
NHS professionals praised the party's NHS reforms.
David Kerr, professor of clinical oncology in Birmingham, said that in 20 years in the health service there had never been a time of "so much commitment.
He continued: "It would be an unmitigated disaster if after all that has been started, we were to stop now and cutback on cancer funding."
In a direct appeal to voters, Mr Blair said: "If you want an extra 10,000 doctors in the NHS, then go out and vote for them.
"If you want an extra 20,000 nurses in the NHS, then go out and vote for them.
"If you want more equipment, more hospitals, then go out and vote for them.
"And if you want to vote against £20bn of Tory cuts, then go out and vote against them."
He urged voters never again to return to the 1980s agenda of "boom and bust economics and "chronic underinvestment in our public services."
Health Secretary Alan Milburn said: "A vote for the Tories is a vote for NHS cuts.
"A vote for Labour is a vote to put the NHS first."
Later in Rugby, Mr Blair said the election would be decided by the voters, not opinion polls.
But the parties face voter cynicism, according to a new survey.
Even those who intend to use their vote are not convinced it will make a difference, says an ICM poll published by the Guardian Unlimited website.
Of the 1,000 random adults interviewed this weekend, 40% of those intending to vote thought it would make no difference.
That rose to 47% among 18 to 24-year-olds and 48% among 25 to 34-year-olds.
However in a speech in the marginal seat of Birmingham Yardley, Mr Blair said that it was "self indulgent rubbish" for commentators to say it did not matter who was elected.
"For the vast majority of people who need their children to be educated in state education and who need the NHS then I tell you this election matters," he told an audience of Labour supporters.
And as the Labour leadership continued with its last-minute push for votes, Cabinet Minister Mo Molam broke away from party policy to support proportional representation.
She told the website ePolitix.com that a change to the electoral system might counter apathy.