Monday’s House of Lords second reading debate of the Marriage (Same Sex Couples) Bill will coincide with a rally outside Parliament organised by equality campaigners.
It will take place by the statue of George V in Old Palace Yard, diagonally opposite the main entrance to the House of Commons at 5.30pm.
Human rights campaigner Peter Tatchell said: “It is important to have a visible presence for equal rights, to counter a planned protest the same night by anti-gay Christian fundamentalists.
“They want us to remain second class citizens, banned by law from marrying the person we love. In contrast to their intolerance, our rally affirms love and equality for everyone.”
He added: “It is uncertain how the House of Lords will vote. We don’t know the extent of the opposition. It would be a big mistake to assume that equal marriage is a done deal.”
Westminster commentators believe there is a comfortable majority for equal marriage in the Upper House.
However, on Wednesday, Labour’s shadow equalities minister Baroness Glenys Thornton warned that with Monday’s debate expected to last well into the early hours of Tuesday morning, a 2am vote could be “very risky” as frail and elderly peers, as well as those who live far away from central London, may not be able to turn up to vote in favour of the bill.
Several supporters of the bill would like to see the second reading debate commence at an earlier time rather than current allotted 3pm start.