Britain’s young adults, who for much of the 20th century enjoyed living standards well above average, have been displaced by the rise of the comfortably-off pensioner in the most dramatic generational change in decades.

Average twentysomethings have seen their living standards slip from a position of comparative affluence to well below par over the past 35 years as average pensioners have enjoyed a rapid rise up the national league tables of incomes, according to Financial Times research.

The findings based on official incomes data on over 800,000 households from over 50 years of income distribution statistics held at the UK Data Service, highlight the disunity between the generations in the UK.

They come as David Cameron intensifies his efforts to woo older voters, pledging to protect pensioner benefits costing billions from any cuts if he wins the May election. It was right to preserve benefits for those that “made this the great country it is today”, he said on Monday, as he promised to preserve free bus passes, free television licences and the winter fuel payment for older people.

His pledge suggests the winning streak could continue for those born in the 1940s and 1950s at the expense of those born in the 1980s and 1990s.

The young and carefree used to have higher living standards than most in Britain. Despite the trials of inflation and unemployment in the 1960s and 1970s, people aged between 20 and 25 with average incomes after housing costs were better off than at least 60 per cent of population.

But a gradual slide, accelerated by the recession, has pushed the average young adults’ living standards so far down that they can now expect only 37 per cent of the population to have lower incomes after taking into account housing costs in 2012-13.

Interactive graphic Old displace young on the income ladder How the generational income gap has changed since 1961 Explore graphic

Replacing the young in the premier league of living standards have been people in their 60s and 70s. The average 65-70-year-old used to have lower living standards than 75 per cent of UK families. Now people in the same age group can expect to be almost in the top 40 per cent of family incomes.

The pattern of gains for the old at the expense of the young is repeated for rich and poor alike, but it is strongest for average and poorer families.

Those born in the 1940s belonged to a particularly lucky generation. On average they were relatively rich as young adults and remain relatively rich today. Those born in the 1980s and 1990s, however, have missed out on the former experience and have uncertain prospects as they age.

A major reason for the shift is the rise in house prices in recent decades. Many older people bought cheap and have locked in sizeable gains, although, with people living longer, some are now facing the prospect of having to sell those homes to pay for expensive care.

With little sign that recent generations of young adults are catching up, there are indications that this generation will remain disadvantaged, experts say, with little chance of their becoming silver success stories. Ashwin Kumar, director of Liverpool Economics and a former chief economic modeller at the Department for Work and Pensions, said that an increase in the proportion of people who never get on to the housing ladder would reduce the numbers who can expect “comfortable retirements”.

Angus Hanton, co-founder of the Intergenerational Foundation, said if the government did not take action to redistribute resources and benefits more fairly across age groups, “young people may want to tear up the social contract between generations”.

The coalition government has exacerbated the intergenerational divide, says Andrew Hood of the Institute for Fiscal Studies. “Since the recession, we have seen much stronger labour market performance of older adults and on top of that the government has chosen to focus cuts on working-age benefits”.