David Cameron was today presented with a mass petition opposing plans to introduce same-sex marriage.
The Coalition for Marriage (C4M) handed in the 500,000-strong petition to Downing Street this afternoon.
Mike Judge, spokesman for C4M, said: "I think marriage is incredibly important. Its definition predates the Government and the Christian church and I don't think it's for politicians to redefine it."
The group is backed by former Archbishop of Canterbury Lord Carey, who described plans to introduce same-sex marriage as a "hostile strike".
Mr Judge, 35, agreed with Lord Carey's description, adding: "You can't redefine marriage and it's a big step for a government to take, particularly one that never commanded a majority.
"It wasn't part of its manifesto, it wasn't part of the coalition's programme for government and they have no popular mandate.
"If they were to hold a referendum I am confident that the British people would say we are happy with marriage as it is."
Newly married couple Rhys and Ester Curnow, both 23, from Newcastle, joined campaigners in Downing Street this afternoon to petition against the legislation.
The couple, who said that marriage is very important to them, were banned from carrying a bouquet of flowers into Downing Street as no props were allowed inside. It had to be left outside on the street.
Mr Judge said: "I don't know what could be more traditional than a bouquet of flowers."
The full petition contains more than 553,300 names and addresses of MPs and members of the public.
Alistair Thompson, spokesman for the group, said it is not a religious campaign and it has gathered support from a "coalition of people from different backgrounds".
In response to the Government's consultation on gay marriage, which closes on Thursday, Dr Sharon James, a senior spokeswoman for C4M, said: "We've got over half a million people who are saying they believe in marriage, and this isn't just religious people but people of no faith, gay people and straight people.
"We believe passionately in marriage. It's much bigger than the church and the state and it goes back to the beginning of human history."
Dr James added: "The most outrageous thing today is that Mr Cameron said they are a Government who are going to prevail and they are going to introduce same-sex marriage. The consultation hasn't even closed yet.
"It's undemocratic and I think people up and down the country are saying 'what an arrogant Government'.
"This consultation was launched with very little publicity. It's almost as if they want to sneak this thing in without a fuss and without people noticing."
Jim Dobbin, Labour MP for Heywood and Middleton in Greater Manchester, said: "I believe in marriage. In my view marriage is between a man and a woman. I don't want to see it redefined. Even in gay communities very few people want a civil partnership."
Mr Dobbin, who joined other MPs including Conservative Congleton MP Fiona Bruce and Labour Bootle MP Joe Benton in signing the petition, added: "The whole aim is to get the Government to sit up and listen. A lot of Conservatives will vote against the proposals and I have heard a lot of noise from Labour against it too.
"I know that in my constituency very few people would support it."
Dr James, who has recently completed a PhD in government family policy at the University of Wales, added: "I think the overwhelming majority of ordinary people think this is of complete irrelevance.
"When it is explained to people that gay people have rights to civil partnership then the vast majority of people would say, 'Why bother messing around with redefining marriage?'
"We have to give the full picture."