Peers are facing a parliamentary marathon as they debate a fresh move to give people with terminal illness the right to die.
A list of around 130 peers have put their names down to speak on Labour former Lord Chancellor Lord Falconer of Thoroton's Bill in a debate expected to last for 10 hours.
The Assisted Dying Bill proposes allowing doctors to prescribe a lethal dose to terminally ill patients judged to have less than six months to live.
Lord Falconer's previous attempts to get the legislation onto the statute book have always run into fierce opposition and a lack of parliamentary time.
Opponents of the Bill have indicated they will not vote it down at this second reading, but the legislation is likely to face a string of amendments if it gets to committee stage.
Speakers due to take part in the debate include Lord Carey of Clifton, the former Archbishop of Canterbury, who said last week he had changed his mind on the issue, after considering cases like that of locked-in syndrome sufferer Tony Nicklinson and "the reality of needless suffering" and would back the Bill.
But the current Archbishop of York, Dr John Sentamu, is expected to argue strongly in favour of the status quo.
His opposition to the legislation will be supported by former president of the Royal Society of Medicine Baroness Finlay of Llandaff and former president of the Royal College of Psychiatrists Baroness Hollins.
Baroness Campbell of Surbiton and Baroness Grey-Thompson, two disabled independent crossbench peers, are also expected to speak strongly against the legislation.
Other speakers include former director of public prosecutions Lord Macdonald of River Glaven, former heads of the Metropolitan police Lord Stevens of Kirkwhelpington, Lord Blair of Boughton and Lord Condon, television fertility doctor Lord Winston, former chief executive of the NHS Lord Crisp and former Cabinet ministers Lord Baker of Dorking, Lord Tebbit, Lord Mackay of Clashfern and Lord Mawhinney.
Government chief whip Baroness Anelay of St Johns told peers yesterday that they would be advised to keep their speeches to four minutes in an attempt to allow the debate to finish by 8pm. The number of speakers is believed to be the most ever to take part in a one-day second reading debate.
Peers and MPs - if the Bill reaches the Commons - will be given free votes on the issue, as it is a matter of conscience.
But Prime Minister David Cameron on Wednesday spoke of his "worry" about legalising euthanasia, saying he was "not convinced that further steps need to be taken'', and that "people might be being pushed into things that they don't actually want for themselves".
Care minister Norman Lamb has spoken in favour of the legislation and said his view as an MP rather than as a minister was that people should be able to "make their own decision about their life".
A ComRes poll for ITV this week found that 70% of Britons would support allowing assisted dying under the measures being proposed, with 10% disagreeing.
But some 47% said they believed legalising assisted suicide would ''inevitably'' lead to some vulnerable people opting to end their lives to avoid becoming a burden on their loved ones.
Lord (Charles) Falconer told the BBC Radio 4 Today programme that the Bill would provide "a limited change in the law, so that, for those people who are dying, if they choose to take their own lives rather than scramble for those last few days or last few weeks, subject to proper safeguards, that option should be open to them".
The Labour peer said he was first prompted to pursue a change in the law by personal experiences, but said he did not want to discuss them.
He added: "I'm very keen to press this Bill, not just because of my own personal experience but because of widespread research and talking to people over a number of years.
"It's incredibly important that the law that is drafted is compassionate but also safe."
But Baroness Campbell, who has a progressive disability and campaigns on behalf of people with terminal illnesses, said she was not satisfied by safeguards, such as limiting assisted suicides to people who have been given less than six months to live.
She told Today: "My fears about this Bill are because, unfortunately, I don't believe it's safe in any degree. I've looked at all the safeguards.
"I've been given six months to live probably about five times in my life - the last time a few years ago. It didn't happen... It's difficult, if not impossible, to predict when you're going to die.
"I have to have absolute faith that my doctors will be there for me, that they will not give up on me and that they will not think the best thing they can do is help me to die."
Lady Campbell added: "People who think they are at the end of their life will feel that this is their only option and they will find two doctors to help them... How does Charlie know that I haven't spent one or two years feeling so desperate I just wanted it to stop? The only thing I could rely on was that the people who were there to protect me will not give up on me. I would be scared of this law because I might take advantage of it."