A tax break for married couple was part of the Conservative manifesto for the 2010 general election. Under the heading 'Reform tax and benefits to help families and pensioners' in said:
Today, Labour’s tax and benefits system rewards couples who split up. a Conservative government will end the couple penalty for all couples in the tax credit system as we make savings from our welfare reform plans.
We will recognise marriage and civil partnerships in the tax system in the next Parliament. This will send an important signal that we value couples and the commitment that people make when they get married.