The future of gay marriage in England and Wales is on a knife-edge with campaigners warning it could all come down to the vote of just a few Lords.

Gay Star News can reveal a headcount by experts in parliament indicates there will be a slim majority in favor of same-sex marriage in the House of Lords – but it may be as small as 10 out of a chamber of up to 763.

Meanwhile Out4Marriage, in it’s public list, has 133 peers for gay marriage, 46 against with 585 undecided.

The Marriage (Same Sex Couples) Bill for England and Wales has already been passed by the elected House of Commons.

As an unelected chamber, the role of the House of Lords is, by convention, seen as reviewing and scrutinizing Commons legislation.

But this time Lord Geoffrey Dear, retired police officer and leading opponent of same-sex marriage, has tabled an amendment to stop the bill dead in its tracks.

A two-day debate on Monday and Tuesday (3 and 4 May) will see Lords argue the merits of the bill late into the night on the first day. It will then culminate in a crunch vote on Dear’s motion at around 5pm on the second day.

It is set to be stormy with 80 peers due to speak. But it will give opponents and gay marriage supporters the chance to debate the broad principle of marriage equality.

If Dear wins his vote on Tuesday, the bill won’t go through to committee and report stage, where it is scrutinized in detail.

If he loses the vote on the amendment, the house should nod through the second reading of the bill and committee and report stage will be on 17 and 19 June.

Unlike in the Commons, where this was done by a small group of Members of Parliament (MPs), the whole of the House of Lords will take part in these stages, which will be done on the floor of the house.

With so many more opponents able to take part, there is the risk of more wrecking amendments. The one least likely to succeed is the watering down of the legislation so it offers ‘civil unions’ rather than equal ‘marriage’.

Other greater threats would be opt-outs for public marriage registrars and state school teachers, so they didn’t have to wed gay couples or even tell the truth about the legal status of marriage for gays, lesbians and transgender people in schools.

Campaigners for marriage equality remain confident about the process but warn it will be historically tight.

They remind people the Lords did wreck the Civil Partnership Bill a decade ago, although it did eventually pass, giving same-sex couples rights reflecting marriage in a separate-but-equal system.

The debate in the Lords has already been lengthened from one day to two, to avoid a vote at 2am in the morning, which may have seen gay marriage supporters give up and go home while stalwart equality opponents stuck around to kill the bill.

Head of policy for Stonewall, the UK’s leading gay lobby group, Sam Dick said: ‘We expect a tough fight in the House of Lords next week and we’re working tirelessly to help the bill get through second reading.

‘By supporting this modest measure peers will demonstrate that they’re in touch with British public opinion in the 21st rather than the 19th century.’

Meanwhile James J Walsh of Out4Marriage said volunteers had worked around the clock to get a website ready to allow LGBT people and their friends and allies to ‘Lobby a Lord’.

He said: ‘We always knew the battle in the House of Lords was going to be the harder one which makes us nervous but also makes us dig in a bit harder. This is the reason why people have to lobby.’

And referring to Dear’s attempt to stop the Lords scrutinizing the bill in detail he said: ‘Part of the reason we have a House of Lords is when you have an unelected second chamber they should be there to stand up for the rights of minority groups and have a focus on scrutinizing. So by saying we don’t need to discuss this would be wholly undemocratic.’

He feels the Lords should respect the elected Commons and the fact that polls show the majority of Britons are in favor of gay marriage equality.

The bill has also stirred up other controversy.

Notable has been the refusal of Baroness Sayeeda Warsi, the Minister of State for Faith and Communities in the Lords to steer her own government’s bill through the house.

The National Secular Society (NSS) has called for her to be sacked and her position to be scrapped as a result.

Terry Sanderson of the NSS, who is also a gay rights campaigner, said: ‘It is simply not acceptable for a minister to allow their religion to dictate their political actions when it is to the detriment of a minority whose rights she has been charged to protect.’

If the legislation makes it through the Lords on schedule, it will be passed by this summer and the first fully equal gay marriages will be in summer 2014.

If Dear and other opponents in the Lords scupper it, Members of Parliament can still force it through using the Parliament Act which prevents unelected Lords blocking the will of elected MPs. GSN understands any MP could use the Parliament Act on the bill, as it was passed in the Commons on a free vote.

Meanwhile, as peers debate the bill, anti-gay opponents, headed by Christian groups, and LGBT marriage supporters will protest outside parliament.

The London Gay Men’s Chorus is planning to sing outside the chamber to rally support.

You can find out more about the LGBT marriage vigil outside the Lords here. The Facebook event page is here. The hashtag on Twitter is #LordsVigil.

Separate legislation on marriage equality for Scotland will soon progress through the Scottish Parliament.