The analysis revealed that women born between April 1952 and July 1953 could miss out on £6 per week, or £310 a year due to the fact that they will reach the state pension age before the proposed start date for the new single-tier state pension of £144 per week.
Men born between these dates will not be affected as they reach state pension age after the proposals come into effect in April 2017.
Shadow pensions minister Greg McClymont said 80,000 of the 430,000 affected would be further hit as the increase in their retirement age coincides with April 2017, and would lose on average £9 per week. This came just two years after hearing of the increase in their retirement age.
Speaking in parliament, the Labour MP for for Cumbernauld, Kilsyth and Kirkintilloch East, asked Mr Webb: “Is it fair to penalise these women twice in two years?”
Mr Webb, the Liberal Democrat MP for Thornbury and Yate, said: “To be clear about the particular group to which the honourable gentleman refers, their pension ages increased by a maximum of six months under the 2011 pensions act.
“The vast majority of those 80,000 would be worse off if we treated them the same as men, which is what he seems to be calling for. It was not clear what else he was calling for, but treating them the same as men would leave them worse off than they are now.”
Mr Webb later gave evidence the final oral evidence session by the Work and Pensions Committee who are reviewing the plans, calling the single-tier pension a “perfect compliment to auto-enrolment”.
He said that the changes would put an end to unnecessary complexity and would therefore be “fundamentally fairer”.
Ros Altmann, director general of Saga Group, said: “It seems ironic that a new state pension system, that was supposedly designed to help ensure women could receive better state pensions in their own right, has ended up penalising a particular group of women relative to men of the same age.”