Labour’s shadow equalities minister Baroness Glenys Thornton says David Cameron has been “absolutely brilliant” in his support for equal marriage, but warns a late night vote in the House of Lords next week could put the same-sex marriage bill at risk.

Following its successful third reading in the House of Commons, the House of Lords will debate the Marriage (Same Sex Couples) Bill on Monday.

At least 80 peers have asked to speak in the debate which begins at 3pm – meaning it could last well into the early hours of Tuesday morning.

Labour has warned a 2am vote could be “very risky” as frail and elderly peers, as well as those who live far away from Parliament, may not be able to turn up to vote in favour of the bill.

Shadow equalities minister Baroness Thornton said the debate should instead be stopped before midnight on Monday and then started up again on Tuesday morning.

Many would also like to see the second reading debate start at an earlier time.

Crossbench peer and equal marriage opponent Lord Dear has put down a “fatal motion” to deny the bill its second reading.

The former chief constable of the West Midlands said he expected the final result to be much closer than in the Commons where the bill received a majority of 205 votes on Tuesday 21 May.

“I don’t think it will be a landslide either way,” he told the Huffington Post UK.

“The one thing I can be sure of there is a great deal of dissatisfaction with an ill thought though bill.”