Mr Harrington is not unsympathetic.
But his response to the issue is blunt: Waspis will get no more from the Government.
He pointed out that a large part of his job was to make the state pension more affordable for taxpayers and generally sustainable.
He said: “I don’t like giving people false hope or straws to clutch on to. I think too many politicians do that. It’s easy when you’ve got people in front of you, or when you’ve got people writing to you or lobbying you.
“The Government’s position is very clear: it will be making no further changes in this field – and that’s it.”
Ms Keen is undaunted. She said: “I don’t know how he can say that. MPs are getting as angry as we are about the Government’s failure to listen to us. He says there is no money, but we know money can be found if ministers really want it.”
On the issue of cost, Mr Harrington said that in 2011, when the Government proposed a further two years’ wait for the state pension, but then relented in the face of protest and reduced the delay to 18 months, the cost of this change of tack was more than £1bn.
The cost of the “bridging pensions” being sought by Waspis would be far higher. Those whose pensions have been delayed by the maximum six years could be due more than £40,000 each.
Steve Webb, who was pensions minister in 2011 and is now director of policy for pensions provider Royal London, said: “With every passing year more and more women reach retirement age.
“The Government would end up writing cheque after cheque. It would be impossible to distinguish between those who genuinely did not know about the changes and those who did.”
Ms Keen said: “People ask us to cost the process of paying us our pensions, but how can we do that? We are ordinary people. Why can’t the Government’s actuaries cost it?”
Malcolm McLean, a senior consultant at Barnett Waddingham, a pension firm, said: “There is a lot of sympathy for Waspi women but I don’t think it was ever on the cards that they would be treated as they would have been before the changes.
“I would have thought, however, that there could have been a compromise made, as this was clearly not handled well in the early stages.”
The pension minister’s other problems
Richard Harrington has other difficulties to deal with apart from fending off angry Waspis.
It falls to the Treasury, rather than his department, to determine the tax aspects of pension saving.
So any overhaul of pensions tax relief, for example, which is the process by which the Government tops up savers’ pension contributions, is outside Mr Harrington’s remit.
But he is responsible for the state pension age and there is a distinct possibility that this may be about to rise, even further, for younger generations.
The state pension age is currently 65 for men and just over 63 for women. The pension age for women will keep rising steadily every few months and equalise at 65 for both sexes in 2018. It will then increase every few months for men and women, reaching 66 by 2020.
The next stage of planned increases, towards age 67, is due to begin in 2026 and conclude in 2028.
But next month will see the publication of the interim findings of the Cridland Report, an independent examination of the state pension age and how it might be adjusted in future in the face of rising longevity and an ageing population.