As a Conservative backbencher in 2003, David Cameron voted in favour of the retention of Section 28, the law that banned schools from "promoting" homosexuality as a "pretended family relationship". It is a mark of how much has changed since then that he now leads a government that has brought forward a bill for the introduction of equal marriage.
Much of this change is due to a dramatic shift in social attitudes, particularly among the young, one seen across the western world. But while governments reflect the culture of a country, they also help to shape it and on the day that MPs vote for the first time on the Marriage (Same Sex Couples) Bill, the role of the last Labour government in advancing gay equality deserves to be recalled.
It was the Blair administration that equalised the age of consent, abolished Section 28 (a measure that Cameron has rightly apologised for supporting ), repealed the ban on gays and lesbians serving in the military, gave same-sex couples the right to adopt, outlawed discrimination in the workplace and in the provision of goods and services, and established civil partnerships. It is a record that Ed Miliband has rightly described  as "proud". Change may have come under a Conservative government but it would not have been as swift or as deep.
It is because gays and lesbians have already achieved equality in so many other spheres of life, that the extension of marriage to them now seems entirely natural. Cameron's bill is but the cherry on the wedding cake.
Had the last Labour government not devoted so much time and effort to promoting gay rights, it is doubtful whether the Conservatives would now be introducing equal marriage. So, while Cameron deserves praise for defying the opposition of so many of his MPs, all who support gay equality owe a debt of thanks to Tony Blair today.