Women hit by the state pension age rise could alter the result of the forthcoming general election, say experts.

The increase from age 60 to 66 has affected nearly 4 million women, in some cases causing homelessness and destitution.

Campaigners argue the amendments unlawfully discriminate against females born in the 1950s.

Women affected by the increase lost their landmark High Court battle against the government last month but have applied for permission to appeal.

Polling experts and campaigners told The Independent women bearing the brunt of the overhaul could have a substantial impact on the outcome of the 12 December election.

Joanne Welch, founder of Backto60, said women are saying they will lend their vote to candidates who roll back the changes.

The campaigner said: “[We want a pledge] that if you have lost five years of your state pension, you will get it back. There are almost 6,000 women born in the 1950’s in each constituency across the country on average. If the incumbent MP’s majority is slim, then they can easily sway the result of that constituency.

“It is not only women born in the 1950s. It is now their families and friends too: 3.8 million women can easily turn into ten million with them. What we are looking for is a declaration from party leaders to say exactly what they will do. We want people to understand the power of our voting bloc.”

Ms Welch would not comment on the respective parties policies on the state pension age until all of their manifestos have been released.

Ms Welch, whose campaign group took the government to court over the issue, fiercely condemned Boris Johnson for performing a “U-turn” on the state pension changes – noting the prime minister had pledged to look at the issue with “fresh vigour” during the Conservative leadership campaign.

Mr Johnson’s official spokesperson said they welcomed the High Court’s judgement last month and said it has “always been our view” the changes made were “entirely lawful and did not discriminate on any grounds”.

Ms Welch said she was “shocked” by the recently leaked internal document from the Tory party headquarters, unearthed by The Guardian, which told conservative candidates in the general election not to add their signatures to particular pledges.

“Avoid signing [pledges],” the document says. “Changes to the state pension age are part of a long-overdue move towards gender equality and will put the pensions system on a more sustainable footing for future generations.”

Ms Welch argued the government had broken the law in not informing women their state pension age had changed – claiming there have been “proactive manoeuvres” not to tell people.

The campaigner said women’s lives had been “annihilated” by the pension adjustments and some were being forced on to the streets and others had accumulating debts. She said one woman she knew had suffered a mental breakdown due to not getting her state pension.

“Another woman told me the changes were her ‘death warrant’,” Ms Welch said. “I can’t forget those words. They literally haunt me. Women are clinging on by their fingertips to stay afloat. They try everything. They sell furniture and jewellery and anything they can. One person told me she had sold her grave plot where she would have been buried next to her parents. Imagine being in debt and then having that emotional hit. Women are being made to feel like they are scroungers when they have been striving their whole lives. It is outrageous.”

The UN Committee on the Elimination of Discrimination against Women has said the rise in the pension age has added to “poverty, homelessness and financial hardship among the affected women”.

The Department for Work and Pensions was taken to court by two claimants who said raising their pension age “unlawfully discriminated against them on the grounds of age, sex, and age and sex combined” and they were not given adequate notice to adjust.

Michaela Hawkins, who has been affected by the state pension changes, said: “I will not support the conservatives because of their track record on women’s rights. They have deliberately exploited women born in the 1950s by taking away up to six years of their state pension for no other reason than we are women who are seen as easy targets.”

Women got their state pensions at 60 until 2010 with rises in the last decade. The retirement age of both men and women is set to increase to 67 by 2028.

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