Pensioner groups fighting the government's RPI to CPI switch for benefit increases took their legal challenge to the Court of Appeal today.
The start of the two-day hearing was combined with a protest outside the court.
In October last year, the the Civil Service Pensioners' Alliance and a range of other pensioner groups applied for a judicial review of the coalition's decision to change the index used to uprate pensions, benefits and tax-credits from the Retail Prices Index (RPI) to the typically-lower Consumer Prices Index (CPI).
The case was dismissed in the High Court but because one of three judges gave a dissenting view the ruling could be appealed.
CSPA general secretary Mike Duggan said: "Before the last election, both the Conservatives and Liberal Democrats promised pensioners that their accrued rights to increases to their pensions would be secure. They have both reneged on that promise.
"The switch from RPI to CPI will have a devastating effect on the retirement incomes of millions of pensioners across the UK.
"The Secretary of State has gone beyond his legal authority in selecting CPI as the indexation for pensions up-rating.
"In our view the legislation makes it clear that indexation should protect the purchasing power of pensions, which the CPI fails to do."
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