It is likely to cost £12 billion more to fund benefits for pensioners by 2019 than it did a decade previously, the director of a leading economic think tank has said.
In six years' time there will be two million more people aged over 65 than there were in 2010, Paul Johnson of the Institute for Fiscal Studies (IFS) said.
To deal with the increasing costs Mr Johnson, writing in The Times, said society has three choices - cutting benefits and services for older people, increasing taxes, or making cuts elsewhere.
Mr Johnson said the choice made by the current Government is "pretty clear" in focusing cuts on people of working age.
He said: "Recent work by my colleagues at the IFS suggests that most people retiring now will be better off in retirement than they were on average over their working lives."
While he hailed that fact as "probably the greatest triumph of social policy during my lifetime", Mr Johnson warned of the costs associated with it.
He cited generous public sector pensions and also said "plans to raise it (the state pension age) by a couple of years by the mid-2020s don't look so radical" when the 10-year rise in male life expectancy is considered.
Research published yesterday by the Joseph Rowntree Foundation found pensioner poverty has fallen over the past decade, but showed there has been a big increase in the number of younger people living in poverty.
Pensioner poverty is now at the lowest level on record and the UK's employment rate is close to a historic high, but incomes are lower than 10 years ago, and average wages for full-time male workers have fallen by £1 an hour to £12.90.