Two votes will take place at the House of Commons tonight concerning same-sex marriage.
The first concerns the second reading of the Marriage (Same-Sex Couples) Bill, which proposes that gay couples can wed, while including a "quadruple lock" for religious groups who oppose such a union.
This will be a free vote and is expected to pass, despite strong opposition from a large number of Conservative MPs in defiance of the Government's appeals.
The second vote will be on how the legislation will be scrutinised as it passes through the Commons - the Government's programme motion - and MPs will be subject to a three-line whip. Less MPs are therefore expected to defy the whip, although strong opposition is still expected.
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.