New figures by the ONS reveal marriage is still the most common way couples live together.
The figures from 2019 show just over half the population are married or part of a civil partnership.
But the proportion of people who are married is slowly declining except for those aged 70 or above.
Women over 70 were particularly more likely to be married or divorced in 2019 than 10 years ago, and less likely to be widowed suggesting improvements in life expectancy.
For younger people in a couple the picture is slightly different. Two thirds of people aged 16-29 co-habit, compared to just 4.5% of those in the over-70s bracket doing so.
Reacting to the figures Harry Benson Research Director for the Marriage Foundation said: "The truth is that while cohabiting may be popular it is also profoundly unstable in the long term. The result is that as time passes, more and more of those who remain as couples are married.
"If you want reliable love, at some stage you have to make a commitment. Whatever people may think about marriage, the reality is that it's still by far the best way to stay together for life."