'It's not like we are all going to be marching into Catholic churches in bridal dresses,' says one gay man at Designer Civil Partnership show

"Let me not to the marriage of true minds/ Admit impediments," declared the bard of Stratford in his 116th sonnet. And at the Globe theatre in central London on Sunday – even as Catholics were being urged from thousands of pulpits across the country to oppose gay marriage – there was no shortage of same-sex couples ready to heed his encouragement.

At the Designer Civil Partnership show at Shakespeare's erstwhile theatre, excited couples discussed the colour scheme of invitations, whether wedding "favours" were a necessary part of the big day – and the decision of the Catholic church to wage war against government plans for gay marriage.

"I think it's disgusting. We are not second-class citizens and the idea that this archaic institution should dictate how we live our lives is appalling," said Matt Turrell, 37, a photographer specialising in civil partnerships. "At the end of the day, the union of two people should be about love. Why should we be denied the right to express that publicly?"

On Sunday a letter from two senior Catholic archbishops was read in 2,500 parish churches during mass, arguing that a change to the law would reduce the significance of marriage. Archbishop Vincent Nichols, the leader of the Catholic Church in England and Wales, and Archbishop Peter Smith, the archbishop of Southwark, urged their flock to sign a petition against the move, telling them it was their "duty to do all we can to ensure that the true meaning of marriage is not lost for future generations".

This has a profound impact on people like Evelyn Len, 29, a practising Anglo-Catholic who is due to marry her partner next May. They will have a civil ceremony, but have found a priest who is willing to do a religious blessing. "I would like to get married in a church, and it's very frustrating because I think lots of priests would like to be able to," she said. She was "at peace" with both her religion and sexuality, she added. "I go by what I think Christ would say. I try and keep that in mind when people get angry about it – people have taken these stances, not God."

Her partner, Shelley Webster, 29, saw the debate in a positive light. "When I was a teenager, I never thought the stage when I would be able to have a civil partnership would come," she said. "We've got a long way to go, and the pace of change is slow, but at least it is happening, it is being discussed."

With a string quartet playing in the entrance hall, intense discussions on whether ushers should wear matching cufflinks, and stalls displaying everything from chocolate macaroons to crystal-encrusted table centre pieces, this was a wedding fair much like any other.

But gay couples are still made to feel excluded because they cannot marry in the same way as heterosexual couples, according to Chris Ford, 30, and his fiance Andrew Ogilvie, 32. The couple, both nurses, were told they could have no religious element to their service and described it as the first barrier they had faced as gay men.

"I was gobsmacked," said Ogilvie. "Automatically you feel second class, that your union is not valued in the same way. It's not like we are all going to be marching into Catholic churches in bridal dresses, but you just want to have the option. Civil partnerships are good, but they are not perfect."

The archbishops' decision to label the changing of the legal definition of marriage a "profoundly radical step", which would strip the union of its "distinctive nature", was hurtful to religious gay people, said Shaz Riley, 46, director of the Butch Clothing Company, who was giving advice to potential brides who wanted to avoid a big white dress.

"I have gay Catholic friends who will be no less than heartbroken at what is happening today," she said. Reacting to the archbishop's comments that "marriage is intended for the procreation and education of children" – and that this should exclude gay people – she said: "It's a very sad day. That the church can tell us we will go to hell, or that we can't have families in this day and age, is astonishing."

She and her partner Sue – who introduces herself as Mrs Sue Riley – had a civil partnership ceremony, but would have preferred to have married. "I refer to her as my wife, she is my wife and we are very happily married, no matter what the law might say."

While the new dean of St Paul's Cathedral the Very Rev Dr David Ison has called on the Church of England to embrace gay marriage, the archbishop of York, John Sentamu, joined the Catholic-led opposition. "I happen to believe that to change the law in the end would be forcing an unjustified change," he told the BBC's Andrew Marr Show. But the prime minister has made his support for gay marriage clear. "We believe people should have the option of civil marriage, irrespective of sexual orientation," a spokesman said this week.

Gino Meriano, 49, founder of the Designer Civil Partnership show, cringes at the term "civil marriage". Doling out fizz to anyone within striking distance ("Clare will see you right for Lambrini"), he is in the unusual position of campaigning for civil partnerships for straight people. "This is the 21st century: gays want marriage, straights want civil partnerships, there are single mothers, there are househusbands. You can't stop the progress of society," he said. "We are not hard done by, we have no chip on our shoulder – we just want equality."

Standing in the sunshine overlooking the Thames from a balcony at the Globe, Natasha Marshall, 31, and Debbie Cross, 38, tuck into the bubbles, chatting about the wedding rings they have just chosen for their civil partnership in September. The pair, who have been together for 13 years, would have liked the option of a civil wedding, but seem unconcerned about the fact that they will not yet be able to have a religious ceremony. "Church weddings are boring anyway," said Cross. "We're going to have a lot more fun than that."