At the time of the 2010 general election, the Conservatives promised a transferable tax allowance worth around £150 to married couples.
The Liberal Democrat leader Nick Clegg ridiculed the proposals as "patronising drivel that belongs in the Edwardian age".
His party later secured a provision in the coalition agreement allowing them to abstain from voting on the issue.
More top news
Americans celebrated 239 years of independence yesterday. Here are some of the best pictures.
England beat Germany 1-0 after extra-time to finish third in the Women's World Cup.
The youngest royal will make her second public appearance later this afternoon when she is baptised in Norfolk.