The UK's fertility rate has been below the level needed for the natural replacement of the population for more than 20 years, Bob Armitage, a statistician with the ONS said.
Women are having children older, with fertility rates falling for women under 30 and rising for those above that age. The proportion of women who never have children has increased and looks set to rise further.
Of those born in 1944 only 10 per cent remained childless. For those born in 1949 the figure is 13 per cent. But for those born in the 1960s, the trends indicate that more than one in five are likely to remain childless, a proportion not seen since the first two decades of the century when the First World War decimated the country's youth and left many women to live out their lives as spinsters.
Many factors may explain the decision not to have children, Mr Armitage said, including women's greater access to both education and employment.
At present, births still exceed deaths because the baby boomers of the 1960s generation are reaching peak childbearing age. But as they age, the smaller numbers born in the 1970s, when fertility fell and then stabilised, are likely to have fewer children overall - producing a population decline in around 2025 as the post-war baby boomers start to die in numbers.
Apart from a statistical blip in 1983, it will be the first time the UK population has fallen in 600 years - since the Black Death in the mid- 14th century.
Italy, Spain, France and Germany all have lower fertility rates than Britain, the first two and Portugal being likely to enter population decline ahead of the UK.Reuse content