The public is still "very much in the dark" about pension reforms to be introduced within weeks, the SNP has warned.
A new flat-rate state pension will be set at £155.65 for those who reach the qualifying age on or after April 6 while the basic state pension is to increase by 2.9% to £119.30 a week.
But Eilidh Whiteford, the SNP's social justice and welfare spokeswoman, told the Commons that "very few people" will receive the new flat-rate and some may receive a lower amount compared with the old system.
She also warned a "two-tier system" could be viewed as operating due to this, noting she believes MPs will be "inundated" with approaches from constituents once these people work out they have been "short-changed" by the changes.
Labour's Andrew Gwynne (Denton and Reddish) also warned a failure to communicate the reforms runs the risk of repeating "mistakes" which have affected women born in the 1950s due to the acceleration of the state pension age.
Speaking in the Commons, Ms Whiteford said she was surprised there was "so little interest" in debating two orders introducing the changes which were tabled by the Government.
She explained: "Not because there are deep-seated, fundamental differences and disagreements on the issues before us, but because given the very significant changes that are about to take effect with the introduction and implementation of a brand new pensions system in just a few weeks time, I'd have thought there'd have been an appetite in the House to debate the issues surrounding that.
"And indeed to raise awareness with the public, who I think are still very much in the dark about the changes and the significance of them for their own lives."
Ms Whiteford said very few people will receive the £155.65 new state pension rate, adding: "Even though the single-tier pension will be higher than the basic state pension, the net amount some people will receive may be less than what they would have got under the old system because of the loss of means-tested benefits.
"Only 22% of women and 50% of men who are going to reach state pension age in 2016/17 will get the new state pension in full."
Mr Gwynne, intervening, told Ms Whiteford: "Is it not the case that it's incumbent on the Government and on ministers to properly communicate these changes because don't we also run the risk of repeating some of the mistakes that have impacted on the Waspi (Women Against State Pension Inequality) women, in that those people will be bitterly disappointed when they realise they're not getting the entitlement they thought they were going to get?"
Ms Whiteford said successive governments have failed to communicate "adequately" with pensioners about a system that is "undoubtedly very complex".
She went on: "We're calling it a single-tier pension and making much of that flat-rate but in reality there is going to be many different rates depending on an individual's personal circumstances.
"In other words, it's not going to be so simple."
Labour said it broadly welcomes the changes although shadow work and pensions minister Angela Rayner added: "What is less welcome is the lack of communication, escalated time-scales, poor management and utter confusion caused by what the former pensions minister, Steve Webb, said was meant to be a simplified system.
"Several aspects of the new legislation will have significant implications for current and future pensioners."
Work and Pensions Minister Shailesh Vara said: "The issue of communication has come up repeatedly, and I just want to say that there is an awareness campaign which is particularly targeted towards those who are 55 and older.
"They will receive a letter providing details of their own state pension, the details for their addresses which we obtained from the payroll and benefits data.
"The first phase of our communications campaign aims to build awareness among those who are of that particular age group - 55-plus - who will be the first to reach pension age after April 2016 and we're encouraging them to get a personalised statement.
"Between September 2014 and October 2015 we have issued nearly 500,000 personal statements.
"We have fact sheets, infographics, videos, calculators, YouTube videos, tool kits for stakeholders and weekly stakeholder bulletins, and of course we'll continue to do whatever is necessary and whatever we can to ensure that people are aware of it."
Mr Vara urged all MPs to ensure they also "do their bit" to raise awareness, adding the new state pension aims to be simpler and clearer than the previous system.
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