On the eve of the Commons vote on gay marriage, Chancellor George Osborne, Foreign Secretary William Hague and Home Secretary Theresa May have made a final attempt to win over wavering MPs by insisting is "the right thing to do".
In a joint letter to The Daily Telegraph, the senior Tories questioned whether it was "any longer acceptable to exclude people from marriage simply because they love someone of the same sex".
Marriage has evolved over time. We believe that opening it up to same-sex couples will strengthen, not weaken, the institution.
Attitudes towards gay people have changed. A substantial majority of the public now favour allowing same sex couples to marry, and support has increased rapidly.
This is the right thing to do at the right time.
Landmark plans to legalise gay marriage got the green light in the Commons, despite a majority of Tories failing to support the Government.
The Prime Minister will read the letter delivered to Number 10, take their views on board, but not change his mind over gay marriage.
Many Conservative MPs just do not understand the move when the tax measure is in the Coalition Agreement.