The shadow chancellor said “ten million pensioners are waking up this morning to the fact they could lose their winter fuel allowance”, which will turn the tides in the favour of Jeremy Corbyn’s Labour.
Mr McDonnell branded the Prime Minister’s plans to remove winter fuel payments from most older people – and charge many more for their care – as “sick and sneaky”.
He claimed this would trigger a mass backlash against the Conservatives, with voters flocking to Labour instead.
Speaking on BBC Radio 4’s Today programme, Mr McDonnell said: “Ten million pensioners are waking up this morning to the fact they could lose their winter fuel allowance.
“We are going to win, we are rising in the polls now that people have seen this Tory manifesto.
“I tell you, 10 million pensioners out there will be very angry. Large numbers of young people will be angry because there is no future for them in this manifesto.
“I think we are going to win – we are going to win on the basis of the positive hope we are giving people.”
Unveiling the Conservative manifesto, the Prime Minister claimed she is getting to grips with the “fundamental unfairness” of Britain’s social system.
Under her plans, she will take the first steps towards removing up to £300 from pensioners from their winter fuel allowance.
Mrs May will also dump the Conservative commitment to restrict the maximum amount the elderly must pay for their care, designed to prevent them from having to sell their homes to pay the bills.
David Cameron previously proposed a cap of £72,000, delayed until 2020, but the Prime Minister will argue that limit is no longer needed.
Instead, she pledged to significantly raise the threshold of personal assets at which people will be eligible for state help with residential care costs from £23,250 to £100,000.
Mr McDonnell argued ten million pensioners would lose out because the Conservative’s proposed to means test for the payments.
One-third of those eligible to claim pension credits did not because it involved filling in a form, Mr McDonnell said.
“It’s about universalism, that phrase that we are will in this together. That’s the basis upon which we’ve created our welfare state,” he added.
The shadow chancellor insisted this is a springboard for Labour to propel themselves to victory and overturn the Conservative’s double-digit lead in the polls.