By politics.co.uk staff
Conservative plans to introduce a marriage tax break have been challenged by a thinktank report arguing marriage is not decisive in making relationships more stable.
David Cameron consistently argued during the general election campaign he wanted to see the government do what it could to help encourage more stable families.
A report from the Institute of Fiscal Studies out today casts doubt on the government's aim of promoting marriage in order to reduce parental separations, however.
The Tory argument rests on the case that cohabiting parents are three times more likely to split up by their child's fifth birthday than married couples.
"The evidence suggests that much of the difference in relationship stability between married and cohabiting parents is due to pre-existing differences between the kinds of people who get married before they have children, compared to those that cohabit," IFS research economist Ellen Greaves said.
Cohabitees are typically younger, less well-off, less likely to own their own homes, have fewer educational qualifications and are less likely to plan their pregnancies than married couples, according to the IFS.
As a result the real difference between the two groups is negligible, its report suggests. The IFS concludes factors other than marriage including age, education and occupation are more important.
The coalition agreement includes a provision allowing the Liberal Democrats to abstain on a married couples' tax allowance.