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
Rape suspects will need to prove to police that a woman consented to sex under fresh new guidance in sex offence cases.
Dippy the Diplodocus is to forced into retirement and moved out of the Natural History Museum's main hall.
Alice Biggar has managed to survive on cheap tins, heavily-reduced supermarket goods and even chicken bones from butchers.