Elderly people represented almost a quarter of Scotland's poor in 2007/8
The UK has the fourth-highest level of poverty among over 65s in Europe, behind countries like Romania, European Commission figures have shown.
The figures reveal many British pensioners are living on incomes far below the national average.
The charity Age Concern and Help the Aged has called on ministers to act.
But the Department for Work and Pensions said even the poorest pensioners in the UK were better off than those living in other countries.
A spokesman said: "In 1997 our pensioners' income was well below the European average. Today their income is nearly 10% higher than the EU average."
The European Commission figures come shortly before the Work and Pension Committee's review of government efforts on pension poverty is published on Thursday.
The EU research, which compares relative poverty in the 27 member states, shows nearly one in three UK over-65s were living in poverty in 2007, the same proportion as in Lithuania (30%), the charity said.
It added that in most leading European economies, pensioner poverty levels were either below or slightly above the EU average of 19%.
Brendan Paddy, from the charity Age Concern and Help The Aged, told the BBC: "The findings are quite shocking, particularly because some years ago we were beginning to see poverty amongst older people in the UK begin to drop, but that progress has now very definitely stalled."
He added: "One of the big contributors has been low take-up of means-tested benefits, and one of the other big contributors has been rocketing food and fuel prices.
"The problem is the people who most need those benefits are the ones least likely to claim them. They're not on anybody's radar; not even ours.
"Also they find the forms and process to actually claim the benefit really off-putting.
"In addition to that, there's some people who are just too proud to say, you know, I'm going to actually apply for this, whereas if it was part of their standard pension they'd accept it as their due."
Recent research by the charity showed one in five people aged 60 and over was skipping meals to save money on food, while two-fifths were struggling to afford essential items.
Shadow work and pensions secretary Theresa May said pensioners had become "the innocent victims of Gordon Brown's recession".
"It's unacceptable that 2.5 million are living in official poverty," she said.
"The reality is that too many of the elderly are stuck in the vicious cycle of poverty because of Labour's complicated and bureaucratic system of means-tested benefits.
"Furthermore, Labour's obsession with pushing up council tax year after year has had a devastating impact on elderly people on fixed incomes."