Prime minister David Cameron has urged reluctant Tory MPs and members to support gay marriage.

Giving his keynote speech at the party conference in Manchester, Mr Cameron urged the party to back the move because of its Conservatism, not in spite of it.

Last month, ministers announced that a consultation would be held on how to introduce same-sex marriage before 2015.

The prime minister, who backed committment between same-sex couples in his 2005 speech, told supporters today: “I stood before a Conservative conference once and I said it shouldn’t matter whether commitment was between a man and a woman, a man and another man or a woman and a woman.

“You applauded me for that. Five years on, we’re consulting on legalising gay marriage.

“And to anyone who has reservations, I say this: Yes, it’s about equality, but it’s also about something else: commitment. Conservatives believe in the ties that bind us; that society is stronger when we make vows to each other and support each other.

“So I don’t support gay marriage in spite of being a Conservative. I support gay marriage because I am a Conservative.”

The camera then cut to Samantha Cameron applauding her husband’s remarks as members cheered and clapped.

In the 50-minute speech, Mr Cameron focused on overseas aid, free schools, housing, community spirit and the economy.

A controversial line about telling families to cut their personal debts and store cards was removed and replaced with the assertion that households were already doing so.

The prime minister also cracked some jokes at the expense of his cabinet members.

Describing how Conservatives had been recording books for the blind, he said that Chancellor George Obsorne could record ‘The Man Who Would Be King’ and Boris Johnson could record ‘The Joys of…. Cycling’.

Themes of the speech included leadership, discipline and optimism.

He promised a “new Tory housing revolution” and vowed to cut red tape to boost business growth.

Mr Cameron said: “The critics will say to me: what about workers’ rights? But the most important worker’s right of all is having a job in the first place.”

He also called to businesses to offer more apprenticeships, promising that the government would fund places if companies “show more leadership”.

On education, he said that for too long, society had come to expect less from poor and ethnic minority children.

He said: “I am disgusted by the idea that we should aim for any less for a child from a poor background than a rich one. I have contempt for the notion that we should accept narrower horizons for a black child than a white one. Yes it’s the age-old irony of the liberal left: they practice oppression and call it equality.”

Praising free schools and academies, he called for more business and entrepreneurs to assist in setting them up.

Mr Cameron concluded: “Britain never had the biggest population, the largest land mass, the richest resources, but we had the spirit.

“Remember: it’s not the size of the dog in the fight – it’s the size of the fight in the dog. Overcoming challenge, confounding the sceptics, reinventing ourselves, this is what we do. It’s called leadership.”