Almost twice as many women, including tens of thousands of Scots, will lose out under new plans to fast track a £144-a-week flat-rate pension.

About 720,000 women born between 1951 and 1953 will not be eligible for the new payments, even though men their age will, according to research by the House of Commons library.

The number is almost twice as high as the around 400,000 who would have missed out under the Coalition's original plans.

The change, triggered by a decision to bring in the new state pension in 2016 not 2017, means around 70,000 women in Scotland will lose out.

The research was released as MPs called on the UK Government to get a grip on the plans.

Labour's Shadow Pensions Minister Gregg McClymont said the Coalition was "discriminating against 720,000 women over all who are set to miss out on the new state pension while a man of the same age will receive it".

He described the move as "another blow to people so close to retiring". And he claimed the Government's pensions policy was in "utter disarray" after ministers announced in last month's Budget they were bringing forward the implementation of the new state pension.

The report published today by the Commons Work and Pension Committee accuses the Tory-LibDem Coalition of displaying a "cavalier attitude" to the new state pension.

It also calls on ministers to find a solution for what it describes as "another small group of women ... who did not build up their own national insurance record because they had a legitimate expectation they would be able to rely on their husband's contributions to give them entitlement to a Basic State Pension."

Dame Anne Begg, chairwoman of the committee, said MPs supported the principle of the single-tier pension.

She added: "In the short to medium term it will mean more state pension for many people, particularly the self-employed and women and carers who have been low-earners or had gaps in employment. But this is a major reform, which will affect all 40 million people of working age. Although the end result will be simplification, the transition period will be long and complex."

An impact assessment of the original plans warned that most people, especially those who were further away from retirement, would be forced to pay more for their state pension.

Those who have already reached pension age before the new system comes into force will also not benefit.

When the plans for the new pension were first set out, ministers said they would not come into force until 2017 to allow companies time to prepare for the change.

But the decision to bring the start date forward to 2016 was confirmed by the Chancellor in his Budget last month.

With the introduction of the new single-tier pensions, ministers will abolish the second state pension, meaning some – mainly higher earners – will see their income in retirement fall.

The flat rate will be worth £144 in today's money, estimated to be around £155 a week by 2016.

A spokesman for the Department of Work and Pensions said the committee had been "broadly supportive" of the Government's approach.