Writing for the Guardian, Abbott and Leigh - the mother and father of the house - said there had been insufficient scrutiny of the bill and urged parliament to instead focus on better health and care services.
Four influential new Labour MPs said they had also decided to oppose the bill amid concerns about the process and the pressure it has put on new parliamentarians.
A vote on legalising assisted dying is to be held on Friday 29 November. It is a free vote, meaning MPs can support or oppose it. In 2015, an assisted dying bill was rejected by 330 votes to 118, but since then a number of countries have legalised the practice and polls show widespread public support.
About 100 Labour MPs are still believed to be undecided. However, the bill's backers remain confident they can be won over.
Keir Starmer and a majority of the cabinet are expected to support the bill, though there have been highprofile interventions opposing it, including from the health secretary, Wes Streeting.
Questions have been raised about the drafting of the legislation - which is a private member's bill from the Labour MP Kim Leadbeater - and whether it is sufficiently watertight.
The Guardian has learned it was drafted by Dame Elizabeth Gardiner, who retired this year after almost a decade as first parliamentary counsel, the government's most senior and experienced legislative drafter.
Denne historien er fra November 21, 2024-utgaven av The Guardian.
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Denne historien er fra November 21, 2024-utgaven av The Guardian.
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Real Madrid take aim at Uefa in bid to revive Super League
Real Madrid have spelled out their commitment to a restructuring of the Champions League in which the clubs not Uefa are in control - essentially a European Super League 2.0.
United's big reset
Rashford faces cut-price exit as part of club's cultural reboot
England get horror draw with France, Netherlands and Wales
England, the holders, have been drawn in a group with France, the Netherlands and their neighbours Wales for the 2025 Women's European Championship in Switzerland.
Maguire in 'really positive' contract talks with United
Harry Maguire is discussing a new contract with Manchester United that would commit him to at least a seventh and eighth season at the club.
Unal's fabulous free-kick earns Bournemouth a point
Bournemouth simply do not know when they are beaten. The substitute Enes Unal powered an unstoppable free-kick into the top corner, seconds after West Ham snatched an unlikely lead courtesy of a contentious penalty.
'I'm at a turning point - now it's about me playing to see how far I can go'
Emma Raducanu was hit by injuries but now feels she has the setup to be able to enjoy life both on and off the court
Filer brings the thunder after lightning halts Proteas
England will go into day three of the Bloemfontein Test in a commanding position, after bowling South Africa out for 281 and increasing their lead to 145 by stumps.
Stokes' latest injury scare adds to England's bad day
On a day in Hamilton that was already foreboding by way of leaden skies, England's troubles deepened well beyond their bleak position at stumps.
Fury vows to focus on Usyk and cut back showboating
When I look in the mirror I don't see a quitter,\" Tyson Fury says as, having suffered the first defeat of his professional career in a dramatic world heavyweight title fight against Oleksandr Usyk in May, he is about to step back into the fire of their rematch this Saturday night in Riyadh. \"I see a man who would do anything to keep going. If I get knocked down nine times, I'll get up 10. If I didn't want to do that, I wouldn't be a boxer, I'd be doing something else, like playing darts. But this is my job.\"
Athletics has funding cut by £1.75m for LA Games buildup
UK Sport has denied putting UK Athletics on the \"naughty step\" after slashing its funding for the Los Angeles Olympic cycle by nearly £1.75m.