It's set to be a day of drama at Westminster as MPs gather for the second reading of Prime Minister Rishi Sunak's controversial Rwanda bill.

The Tory leader has faced resignations and rebellions over the plan, and has already seen one bill struck down by the Supreme Court.

Defeat could see yet another Conservative leadership election or even a general election - but what's actually being voted on today?

Here's everything you need to know.

What is the vote?

The vote is a second reading of Mr Sunak's controversial Rwanda bill, or the Safety of Rwanda (Asylum and Immigration) Bill 2023 if you want to get all technical about it.

The bill is looking to enshrine into British law the definition of Rwanda as a safe country, which the Conservatives hope will allow them to get past the Supreme Court after it ruled a previous incarnation of the bill unlawful.

When will the vote take place?

The first order of business will be a "reasoned amendment" by Labour against the bill, which will fail.

It's hard to give an exact time for a result of the all-important second reading, but we can expect MPs to vote in the evening with a result likely after 6pm.

That is, of course, if Mr Sunak does not withdraw the bill as sections of his party are keen for him to do.

Why is this so important?

The Herald: Prime Minister Rishi Sunak and Rwanda president Paul Kagame (PA)

It's important for two reasons, one of which is the bill itself and the other is what it means for the Prime Minister.

First let's look at the actual bill.

The UK government is looking to press ahead with a scheme which would see asylum seekers deported to Rwanda rather than having their claims assessed here.

Their claims would then be assessed by the Rwandan authorities and if successful they would be settled in the African country.

The Supreme Court unanimously found this to be unlawful, stating that people sent to Rwanda would be at risk of refoulment - which means being sent back to the country from which they fled.

The court found that while it is not unlawful to send asylum seekers to a safe third country, Rwanda does not constitute a safe third country.

In response, Mr Sunak is looking to pass a bill which would declare under UK law that the east African nation is safe and thereby circumvent the Supreme Court.

Read More: Rwanda vote: Rishi Sunak bids to see off major Tory rebellion

It would also remove certain sections of the Human Rights Act, meaning people seeking asylum couldn't argue they face refoulment or use modern slavery protections.

Both the scheme itself and the bill have been heavily criticised by human rights organisations and the legal system.

Ian Jeffery of the Law Society said: "Independent judicial oversight is a bedrock of the rule of law and essential to ensuring there are democratic safeguards for individual rights.

"The measures taken in this bill would effectively place government above the law and demonstrate a profound lack of respect for the rule of law and separation of powers.”

Sacha Deshmukh, Amnesty International UK’s chief executive, said: "The Government’s attempt to bypass a clear ruling from the UK’s highest court that Rwanda is not a safe country for refugees smacks of desperation and marks a new level of lawlessness. 

“Dipping in and out of the Human Rights Act or the European Convention of Human Rights is an outrageous attitude toward both domestic and international human rights law.  

“How can we possibly have faith in ministers to protect any of our rights if such a blatant attempt to flout the rule of law is made an Act of Parliament?  

“We strongly urge Parliament to reject this bill - it breaches international law, plain and simple.” 

What does it mean for Rishi Sunak?

The Herald: Rishi Sunak was forced to desperately defend his Rwanda plan on Thursday

The Prime Minister is in a very tough spot with this bill.

He's basically trying to keep both the right of his party and the more moderate faction together.

The latter, represented by the One Nation caucus, say they are willing to back the bill provided there are no amendments which "breach our international obligations or breach the rule of law".

On the other hand, the European Research Group believes the bill doesn't go far enough and are being coy about whether they'll vote against it.

They're urging Mr Sunak to withdraw it and draft new legislation.

The One Nation caucus comprise about 100 MPs, the ERG is believed to have 34-54.

Read More: Rishi Sunak told Rwanda plan that could seal his fate 'will not work'

Could the bill fail?

No bill has failed at second reading since 1986, so it would be a historic humiliation for Mr Sunak if it did.

All that needs to happen is for 29 Tories to vote against, or for 57 to abstain - and that's eminently possible.

A three line whip will be applied and MPs have been told to cancel any foreign trips, so it's going to be tight. Most expect the government to squeak through, but don't be surprised if they pull the bill should it look like they're going to lose.

What happens if the bill is defeated?

We're probably looking at yet another Tory leadership contest, as it would make pretty clear that Mr Sunak does not command the support of his party.

Some Conservative MPs are even being warned it could bring down the government.

Labour would likely submit a motion of no confidence, though it passing would be unlikely as the Tories are staring at electoral oblivion so backing it would be turkeys voting for Christmas.

Still, it's just about possible there's a world where they collapse their own government to fight the election on Rwanda and 'stopping the boats'.

And what if it passes?

Mr Sunak probably loses, even if he wins.

There's a good chance the Lords will send it right back to parliament, where any amendments would lose either the One Nation Tories or the hardliners.