Jeremy Corbyn will go on the attack today, warning that schools and the NHS will be put at risk if Theresa May remains in Number 10 after the June 8 General Election.
The Labour leader will seek to build on encouraging signs in the polls as he seeks to steer the campaign away from Brexit and on to his favoured battleground of public services.
Mr Corbyn's intervention comes as a seat projection by pollster YouGov suggested that the UK could be heading for a hung parliament, with Labour making gains and Mrs May's Tories suffering losses.
But the Labour leader also faced fresh questions about his approach to immigration as a Labour discussion document indicated the party could open up routes for unskilled foreign workers to come to the UK.
The latest television showdown will take place later, with representatives from seven parties going head to head in a BBC debate.
Neither Mrs May nor Mr Corbyn is expected to take part, with the Tories represented by Home Secretary Amber Rudd instead of the Prime Minister who will be campaigning in the South West.
Liberal Democrat leader Tim Farron, Ukip leader Paul Nuttall, SNP deputy leader Angus Robertson, Green Party co-leader Caroline Lucas and Plaid Cymru leader Leanne Wood will appear, along with a senior Labour politician.
In a speech in London, Mr Corbyn will highlight new analysis showing that under Tory plans, 5.5 million people will find themselves on NHS waiting lists in England by 2022.
Seeking to exploit perceived Tory weakness on social care following the "dementia tax" row, Mr Corbyn will also say 1.5 million older and vulnerable people will not have their care needs met.
In addition, 650,000 children will be "crammed" into primary school classes larger than 30 pupils, and families will be nearly £450 worse off per child as a result of Tory plans to scrap free school meals for 1.7 million children.
"The futures of our NHS and schools are at stake in this election," Mr Corbyn will claim.
"Labour will invest in our people, schools and hospitals. We will cut class sizes, take a million people off the NHS waiting list and ensure people get the care they deserve.
"By contrast, another five years of the Tories would be disastrous for our public services."
For the Tories, Work and Pension Secretary Damian Green accused Mr Corbyn of using "made up numbers" and sought to shift attention back to the looming Brexit talks.
"Brexit negotiations start 11 days after people vote and are crucial to our economic security and the future of public services," he said.
"Made-up numbers from Corbyn cannot hide the fact he's not up to the job of getting the deal we need."
Labour played down reports that Mr Corbyn could open the door to unskilled foreign workers as part of his immigration shake-up, insisting the document leaked to the Daily Telegraph and Daily Mail was a discussion paper and "not a statement of Labour policy".
The potential impact of the shift in poll ratings in recent days was laid bare in modelling by YouGov.
A seat-by-seat estimate for The Times suggested that the Conservatives could lose 20 seats and see Mrs May's majority wiped out, while Labour may gain 28 seats.
The analysis is based on a complex model drawing on 50,000 surveys and suggests Mrs May's gamble of calling a snap election in the hope of a landslide win could backfire spectacularly.
YouGov's analysis puts the Tories on 310 seats, down from the 330 they went into the election with, and 16 short of a majority. Labour would get 257 seats, up from 229.
But YouGov acknowledged there was uncertainty with any model compared to full-scale polling in individual constituencies.
The Liberal Democrats will also seek to put pressure on Mrs May, claiming that her plan to axe free school meals for infants in England will put children's health at risk.
"Theresa May is not only risking the health of some of our youngest children, but she will also create terrible inequality in the classroom," former deputy prime minister Nick Clegg said as the party launched a poster campaign on the issue in London.