People planning to retire this year expect to be living off the lowest average incomes recorded in six years, it is claimed.
The gap becomes much worse when taking into account the effects of inflation's erosion of people's household budgets.
Someone who retired last year would have needed an annual income of £21,400 to have the same spending power as an average person who entered retirement in 2008 on a typical income of £18,700, the Prudential said.
However, the average amount private employees retired on last year was £15,500, leaving them £5,900 worse off in real terms than workers who retired in 2008.
Across Britain there is also a £5,700-a-year difference between the regions with the highest and the lowest anticipated incomes for people retiring this year.
Londoners expect to retire on an annual income of around £18,200 this year, while retirees in the West Midlands have the lowest anticipated incomes, at £12,500.
Post-financial crash, annuity rates have dropped 33% and wiped thousands of pounds off retirees' incomes in recent years, while pensioners have faced a perfect storm of high living costs and low returns on their savings.
Experts also warned that possible changes to the way that Retail Price Index (RPI) is worked out could lead to more people being forced to put their retirement on hold due to the squeeze on their incomes.
Tom McPhail, head of pensions research at financial services company Hargreaves Lansdown (LSE: HL.L - news) , said: "For people approaching retirement, that is a huge blow to their expectations at a time when it is probably too late for them to do anything about it."
Hargreaves Lansdown said that a 65-year-old man with a £100,000 pension pot could have secured an annual income of £7,855 by buying an annuity in the summer of 2008 but if he was doing so in December 2012, that figure would have fallen to £5,338.
Quantitative easing (QE) has been blamed for pushing down annuity rates which set the size of someone's retirement income for life.
QE makes it cheaper for companies to borrow by pushing down the yield on government bonds, but annuity incomes are also based on these yields, meaning that new pensioners see their incomes reduced.
The Office for National Statistics has also been consulting on changes to the RPI and the recommendations from this will be announced on Thursday.
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