It said ‘period' life expectancy at age 65 in 2012-13 was most recently estimated to be 18.3 years for men and 20.6 years for women - significantly below the respective 19 years and 21.3 years reported in the ONS's forecast published in 2009.
Period life expectancy is a less common interpretation of life expectancy which calculates mortality rates for all ages in the same year.
Richard Willets, director of longevity at Partnership, said: "Have we have been over optimistic about life expectancy in the UK? Or is this simply a plateau and we will see a return to growth in years to come?
"While this is unlikely to have a significant impact on the man in the street in the immediate future, if this trend continues the next generation may see larger private pension pay outs or a static state retirement age. A review of the pension age increases is scheduled for the next Parliament but in the meantime, researchers with an interest in longevity and pensions will be watching the situation closely." As will all of the boomers, and I certainly hope this is not a harbinger of things to come.