The Conservatives are launching a "military-style" operation, including an email blitz, designed to target voters in the crucial constituencies needed to secure a Commons majority.
Top 5 Tory targets
And the Liberal Democrats are focusing attention on Romsey in Hampshire, which they dramatically snatched from the Tories in a May 2000 by-election.
A battle of the rallies will feature later in the day as Tony Blair, William Hague and Charles Kennedy all address gatherings of their party faithful.
The politicians are going into the last 48 hours of campaigning before polling day on Thursday with two national daily newspapers already urging supporters to vote Labour.
But Tory leader William Hague will still forge ahead with a meticulously planned attempt to capture support in more than 150 targeted seats.
" We have not clobbered higher tax earners. We have got no intention of doing so "
Former prime minister Lady Thatcher is taking to the campaign trail again with the same task in mind.
She will be in Romford in Essex, high up the Conservative hit list with its Labour majority of 649 votes at the 1997 election.
'Unanswered' tax questions
The strategy switch follows Mr Hague's appeal on Monday for Labour and Lib Dem supporters to "lend" him their votes to save the pound.
The Conservatives will also be mounting a challenge to Labour over what they call the unanswered questions on tax.
Tony Blair addressed the tax issue himself on Monday night, moving to reassure high earners they would not be targeted if Labour were re-elected.
Labour's 5 most vulnerable seats
He will host Labour's Tuesday morning news conference in Wellingborough, where the party has a majority of just 187.
The electorate will be warned that without voting Labour the Conservatives will gain power - reflecting the party's nervousness over recent days at talk of it winning an "inevitable" landslide.
Labour will declare it wants voters to send the Conservatives a message saying "never again will a party dare to stand on a platform of cuts in schools and hospitals".
Tuesday's campaigning for the Lib Dems has seen them focussing on health and public services, particularly on what they say is Britain's poor record in cancer survival rates.
At his morning news conference, party leader Charles Kennedy turned his fire on his political opponents.
"The NHS has not only been let down by Labour but it has been abandoned by the Conservatives," he said.
Mr Kennedy is travelling on to Romsey, where the Lib Dems are defending a 3,311 vote by-election majority, as he and the other principal party leaders focused attention on key seats.
Mr Kennedy said he was not persuaded that a big Labour majority was "in the bag" and he expected some very "quirky" results on election night.
The Times newspaper, for the first time in its history, offers what it calls a "cautious but clear endorsement of the Labour Party".
The Financial Times has also urged voters to back Labour, repeating the stance taken at the 1997 election.
Meanwhile, almost two-thirds of voters believe the political parties have failed to address the issues most important to them, a new ICM poll for BBC News Online suggests.
The survey, published on Monday night, also suggests that for a large minority (16%) of voters, the campaign has left them less likely to vote at all on Thursday.
Another poll, for ITN's Powerhouse programme, suggests that only 4% of Tory supporters expect a Conservative victory - while 78% think Labour will win.