It’s the most controversial battle over a private members’ bill in parliament for nearly 60 years.

Not since David Steel’s 1967 Abortion Act has a piece of legislation been so potentially consequential.

So don’t expect Labour MP Kim Leadbeater’s Terminally Ill Adults (End of Life) Bill to enjoy a smooth passage on to the statute book.

The potential for dirty tricks, delays and wrecking tactics by opponents during the long parliamentary process is enormous.

In fact, at the 11th hour, a group of MPs opposed to the bill have this week launched a last-minute bid to derail the bill, by tabling a wrecking amendment.

Back in the ’60s, it took Steel, then the baby of the House in his 20s before later becoming Liberal Party leader, 18 months of battling to get his bill through parliament.

During that time, he endured sack loads of abusive hate mail, threats of violence and attempts by opponents in parliament to delay and talk out his bill.

Crucially, a sympathetic Labour home secretary, Roy Jenkins, with whom Steel later formed the Liberal-SDP Alliance, gave the bill vital extra time to complete its stages.

But this time Kim Leadbeater could face an even tougher battle to overcome opposition to her assisted dying bill than David Steel’s abortion fight in the 1960s.

For a start, Sir Keir Starmer’s government has got itself into a mess. Yes, it’s a free vote, but while the PM insists the government is neutral, the Health Secretary, Wes Streeting, is against the bill and ministers are split.

There are claims that Ms Leadbeater was initially encouraged by No. 10 to promote assisted dying, despite never having campaigned on it previously, after she topped the private members bill ballot.

But it’s suggested the Downing Street machine, led by chief of staff Morgan McSweeney, now wants to dump the bill because of fears it could paralyse and overwhelm the government for at least a year.

Shenanigans and parliamentary dirty tricks

So what could go wrong for Ms Leadbeater and her controversial bill? The answer is… a lot, starting with a potentially highly-charged, emotional and unpredictable second reading debate on Friday.

Firstly, it’s a big bill, running to 59 pages and 43 clauses. That’s very long for a private members’ bill (PMB), which are often just a few short and simple clauses.

That plays into the hands of opponents, who claim a five-hour debate on a Friday is grossly inadequate for proper scrutiny.

The wrecking amendment tabled this week “declines to give a second reading” to the bill because of insufficient debate and scrutiny and calls for an independent review and public consultation.

Secondly, there aren’t usually time limits on speeches for PMBs, but there may be this time. It’s estimated that up to 150 MPs have applied to speak, which would mean two-minute speeches!

But both Sir Keir and the commons leader, Lucy Powell, have so far flatly rejected calls from MPs for more time to debate the bill, a refusal that could persuade some doubters to vote against the bill.

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Britain’s longest serving MPs, Labour left-winger Diane Abbott and Thatcherite Tory Sir Edward Leigh have claimed it’s being rushed, which puts vulnerable people at risk.

Last week Sir Edward introduced an anti-assisted dying ten-minute rule bill backed by Ms Abbot and other strong opponents of Ms Leadbeater’s bill: Rachael Maskell, Sir John Hayes, Danny Kruger, Sir Christopher Chope, Sir Julian Lewis, Lincoln Jopp, Martin Vickers, Dame Meg Hillier, Saqib Bhatti, Helen Grant and Sir Roger Gale.

It was a warning of trouble ahead. There’s a real threat of shenanigans and parliamentary dirty tricks by opponents. Scores of worthy pieces of legislation have been killed off by Commons old lags who loathe PMBs.

Thirdly, this tactic, known as filibustering, is to make long, rambling speeches – often lasting for two hours or more – to “talk out” a bill, ensuring that time runs out and it can’t be put to a vote to allow it to progress.

Sir Chistopher, another veteran Tory Thatcherite and one of the Leadbeater bill’s leading opponents, is the most notorious killer of PMBs. Even his fellow Conservative MPs claim he is a parliamentary dinosaur.

Bills he has blocked include a pardon for Alan Turing, banning wild animals in circuses, upskirting, protection for police dogs and horses, protecting girls from female genital mutilation and making abducting cats a criminal offence.

The only way for the proposer or supporter of a PMB to thwart the wrecking tactic of filibustering is to stand up and bellow: “My Speaker, I beg to move that the question be now put!”

It’s called a closure motion and requires the support of 100 MPs, which Ms Leadbeater should be able to muster. But failure to prevent a PMB being talked out is a disaster.

That’s because a bill that fails to get a second reading on its allotted day – even if was No. 1 in the ballot, as Ms Leadbeater’s was – goes to the back of the queue for PMBs, often months ahead, and is probably doomed.

Fourthly, even if Ms Leadbeater’s bill does get a second reading, her troubles could be only just beginning. Because it’s such a big bill, the scope for amendments during its line-by-line committee stage is endless.

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And then, fifthly, there’s the House of Lords, full of pesky bishops, distinguished medics, pedantic lawyers and procedural bores. That’s likely to be a long and tortuous process for the assisted dying bill too.

Senior peers have told Sky News they believe the bill will struggle to get through the Lords, because there’s strong support for leading opponent Baroness Tanni Grey-Thompson, the Paralympic champion.

So even if it does finally become law, this controversial legislation could face a painful journey along the way, a journey that could indeed easily take 18 months.

Ask 86-year-old David Steel about what happened with his life-and-death legislation more than 60 years ago.