Gay rights charity Stonewall is being urged to “end its silence” and support full marriage equality for gay and straight couples.

The organisation successfully fought for civil partnerships but has said in the past that while it is not opposed to marriage for gay couples, it does not see it as a priority and prefers to focus on issues such as homophobic bullying.

An open letter signed by a number of gay rights activists, gay religious groups and individuals will be sent to the charity on Friday to ask it to publicly support the issue.

The letter has been signed by Peter Tatchell, Liberal Democrat MP Steve Gilbert, trans campaigner Christine Burns, human rights lawyer Professor Robert Wintemute and a number of other academics, including Professors Celia Kitzinger and Sue Wilkinson, a British lesbian couple who married in Canada in 2003 but whose marriage is not recognised as such in the UK.

Other signatories include straight couple Tom Freeman and Katherine Doyle, who have been campaigning for the right to a civil partnership, and representatives from a wide number of LGBT faith and humanist groups. An associated Facebook group has over 300 members, many of whom have signed the open letter.

A recent PinkNews.co.uk survey found that 98 per cent of respondents were in favour of allowing gay couples to marry but Stonewall declined an invitation to discuss its stance.

Marriage equality has been backed by all five Labour leadership candidates and the Liberal Democrat party is expected to pass a motion in favour of the change later this month.

The letter claims that “‘separate but equal’ is not equal” and lists problems with the current law, namely that trans people must divorce in order to obtain a Gender Recognition Certificate, that it requires gay people to reveal their sexuality on forms and that it “demeans” couples who have married abroad but are recognised as civil partners in the UK.

The campaign was started by University of Southampton student Andrew Godfrey.

He told PinkNews.co.uk: “We don’t want to attack Stonewall, we just want to open debate and ensure the agenda is not being decided behind closed doors.

“Maybe marriage equality is not a priority for them, but it doesn’t mean they can’t say they support it.

“It is a slightly bizarre situation. Lots of people are confused about why they won’t respond to interview requests and won’t speak out on the issue.”

A Stonewall spokesman said the charity would not comment on letters it had not yet received.

The open letter:

Dear Stonewall,

We are writing to ask you to end your silence and openly support full marriage equality.

A recent PinkNews survey found overwhelming support (98%) for full marriage equality. Other LGB&T organisations, including the LGB&T groups of the three main political parties, have also professed their support. However, Stonewall have declined to do so.

At present, there is segregation between the institution of marriage for opposite-sex couples and the institution of civil partnerships for same-sex couples. “Separate but equal” is not equal, and many couples who wish to have their relationship recognised as a marriage are denied this right (conversely, there are also opposite-sex couples who are denied the right to a civil partnership).

Although civil partnerships were a huge step forward and you are to be commended on your work to bring them about, they do not have the same status as marriage. They confer the same legal rights, but there are nonetheless still some significant differences. For example, transgender individuals must divorce their partner if they wish to obtain legal recognition of their gender change under the Gender Recognition Act. Furthermore, at present revealing one’s status as a civil partner (for instance, on forms) is tantamount to revealing one’s sexuality – often in wholly irrelevant contexts. Finally, it is demeaning to same-sex couples who have legally married in other countries that the UK does not recognise their marriage.

At present, your website contains no mention of your position on marriage equality and you have repeatedly declined to respond to questions on the subject (including an invitation from PinkNews to clarify your stance). If Britain’s largest and most influential LGB rights organisation will not even support the principle of marriage equality, calls for marriage equality from the LGB&T community (and its allies) will be undermined.

You have a duty to the people you represent and we urge you to make your voice heard on marriage equality.

For a full list of signatories, see http://whythesilencestonewall.wordpress.com/, there is also a Facebook group which can be found by clicking here.