John McDonnell has likened stumping up the money to compensate the Waspi women with bailing out the banks after the financial crash.
The Shadow chancellor said Labour’s plans to spend £58 billion compensating Waspi women – who have lost out under changes to how the state pension is calculated – would mainly come from borrowing.
He admitted that it was “expensive” but said it was important to right the “historic injustice”.
“In the normal way, when a government has to meet a historic injustice, often when it loses in the court, we will have to identify that funding either from what headroom we will inherit or we will borrow – and I don’t shy away from that,” he told the BBC’s Andrew Marr programme.
He later went on to say the “bulk” of the cash for the claims, led by the Women Against State Pension Inequality organisation, would “come from borrowing”.
Mr McDonnell said: “This is a historic injustice – I’m clearing up the mess of past Conservative governments and I’m standing by these women.
“I will not be moved from this. It is expensive, it is a lot – but when I say to those women how much this will cost, they turn around and tell me ‘well this government has just given £100 billion away to the rich and the corporations’.
“When the banks failed they found hundreds of billions to pay the bankers. So this is a just cause and I stand with it.”
Some 3.8million women hit by pension age rises will get up to £31,300 under Labour’s plans.
Lifting the threshold from 60 to 65 since 2010 had left many on benefits, while others had to work beyond the age they expected.
The Labour promise comes after women lost a High Court battle after a judge ruled that they had not been unfairly discriminated against.
But those affected claim they did not have enough time to prepare for the age rise.
Campaign groups Women Against State Pension Inequality (WASPI) and Backto60 have led the battle.
The five-year policy will see women born between April 6, 1950 and April 6, 1959 receive £100 for each week of state pension they have lost.
Anyone eligible will start receiving cash within months of a Labour victory at the December 12 election.
The news comes after PM Boris Johnson appeared to backtrack on a pledge to help the women.