Campaigners fighting for compensation after the botched increase in the women's state pension age have called on MPs who previously their pledged support to this week prove they are not abandoning them.

Labour has refused to pay out the compensation recommended by the parliamentary ombudsman but the so-called Waspi women warn that "if ministers think this over, they are kidding themselves".

They want MPs to show up and reaffirm their support in a special debate on Wednesday.

The campaigners say 3.6million women born in the 1950s were not properly told about the increase in the state pension age to bring them in line with men. The ombudsman recommended each of those affected should receive compensation between £1,000 and £2,950.

Angela Madden, who chairs the Women Against State Pension Inequality campaign, said: "Waspi women are furious about the Government's failure to compensate them and many have suffered hugely as a result of the DWP's failure to inform them of state pension age increases. In the absence of a fair proposal from the Government to compensate Waspi women, it is now up to Parliament to find a way to award redress for the injustice we have suffered.

"[This] debate is a vital opportunity for all those MPs who have pledged their support to us to reaffirm their previous promises. All options remain on the table to ensure those affected see the justice they deserve.

"If ministers think this over, they are kidding themselves."

Conservative MP Sir John Hayes, who secured the debate, said that for the Government not to compensate the women is "wholly unacceptable".

He warned: "When people feel decisions are made that are unjust we erode people's trust."

A Government spokesperson said: "We accept the ombudsman's finding of maladministration and have apologised for there being a 28-month delay in writing to 1950s-born women. However, evidence showed only one in four people remember reading and receiving letters that they weren't expecting and that by 2006 90 per cent of 1950s-born women knew that the state pension age was changing.

"Earlier letters wouldn't have affected this. For these and other reasons the government cannot justify paying for a £10.5billion compensation scheme at the expense of the taxpayer."