Members of the House of Lords have put forward more than 900 proposed changes to the law to deliver assisted dying, ahead of a debate on Friday.
Experts believe the number of amendments, which is understood to be 942, is unprecedented, but opponents say significant alterations are needed to ensure any scheme can operate safely.
The volume of amendments has sparked a letter from 65 supportive peers to their colleagues in the Lords, raising concern about possible delaying tactics.
Those opposing the bill have been urged not to “frustrate” the passage of the legislation, which has already gained the approval of MPs.
The House of Commons passed the Terminally Ill Adults (End of Life) Bill in June, and it passed its first stage in the Lords in September.
The required line-by-line examination of the bill that follows was delayed, following an amendment by Labour’s Baroness Berger to allow a committee of peers to scrutinise the legislation further.
Parliament heard officials worked into the early hours of Thursday morning to compile the suggested changes to the bill that flooded in ahead of the next scrutiny stage, known as committee stage, which begins on Friday.
There appear to be seven opponents to the bill who have submitted 579 amendments between them.
According to the parliamentary authorities, while some bills have had more amendments tabled in total at committee stage, it sets a possible record for the number submitted in the first full list of suggested changes.
They say it is almost certainly unprecedented for the committee stage of this type of bill, known as a private member’s bill, which has been put forward by backbench Labour MP Kim Leadbeater rather than the government.
Experts including Matthew England, a researcher at the Hansard Society, said the number of amendments “does appear to be a record, at least in the recent past”.
Others drew comparisons to the bill to take the UK out of the European Union, which had 820 amendments in total.
A peer in favour of the legislation told the BBC that the number of amendments “looks like a delaying tactic to me… It’s obviously not a coincidence.”
Defending the volume of amendments, Baroness Luciana Berger, who opposes assisted dying, told the BBC that evidence to the select committee “strongly refuted any suggestion this bill is either safe or workable”.
“This bill is full of holes which vulnerable people will fall through and be harmed if peers don’t act to change and amend it,” she added.
However, signatories to the letter highlighted how the bill had “already undergone unprecedented scrutiny” and “offers dying people the choice of a safe, dignified end while strengthening protections for the vulnerable”.
Former Royal College of Nursing president Baroness Rafferty was among the 65 peers to have signed, and she was joined by scientist and broadcaster Lord Winston, former Labour leader Lord Kinnock and former Whitehall chief Lord O’Donnell.
They urged opponents to focus on refining the bill to find where “genuine improvements can be made, while respecting both the will of the Commons and the overwhelming support of the public”.
In response to the letter, a source close to peers who are concerned about the bill said: “This letter is making claims directly contradicted by the evidence provided in the last few weeks at the Lords select committee by the royal colleges, professionals and independent statutory bodies.
“Evidence and facts are vital when crafting good legislation.”
The bill is being treated by parties as a matter of conscience, meaning they will not instruct their MPs or peers how to vote.
The bill will become law in England and Wales only if both the House of Commons and House of Lords agree on the final drafting of the legislation – with approval needed before spring next year, when the current session of Parliament ends.
If it does pass into law, the government has four years in which to get an assisted dying service into place, meaning it could be 2029/30 before the first assisted death happens.
The legislation proposes allowing terminally ill adults with fewer than six months to live to apply for an assisted death.
This would be subject to approval by two doctors and a panel featuring a social worker, a senior legal figure and a psychiatrist.
