What happened in the Senate in the early hours of Friday morning?

In the words of Motoring Enthusiast Party Senator Ricky Muir, the upper house was faced with a choice between a "bad decision or a worse decision". He opted for what he decided was the former, and gave the government the final vote it needed for the controversial Migration and Maritime Powers Legislation Amendment bill to pass the Senate, 34 votes to 32. The amended legislation was then rushed through the House of Representatives, which was due to have its final sitting day of the year on Thursday, but returned on Friday to pass it into law in just 12 minutes.

OK, that's the procedural side of it. What does it actually mean?

Along with other recent changes, the bill gives Immigration Minister Scott Morrison unprecedented powers over Australia's response to asylum seekers. The changes include: removing any duty for the government to comply with international law or act fairly when detaining asylum seekers at sea; introducing fast-tracking refugee status determinations, a step Amnesty International says will see some returned to places where they face persecution and torture; blocking asylum seekers' right to claim protection on national interest or character grounds without further explanation.

Asylum seekers will no longer have access to the Refugee Review Tribunal, which has had the power to correct processing mistakes by the immigration department. Instead, they can apply for a desktop review by a new Immigration Assessment Authority, though some groups won't have access to that either.

The law strips out references to the Convention Relating to the Status of Refugees – the 1951 document that defines who is a refugee, their rights and countries' legal obligations of countries.

They are replaced with a new definition of refugee that drops the long-held commitment to non-refoulement – the idea that no-one should be returned to where they may be persecuted.

But isn't this bill all about temporary protection visas?

Yes, that's another part of it: temporary protection visas, which were in place under the Howard government and abolished under Kevin Rudd, will be re-introduced for about 30,000 asylum seekers who arrived before July 19 last year. It means asylum seekers who have been detained on Christmas Island will be transferred to the mainland, released into the community and be able to look for work. Those already in the community on bridging visas who are found to be refugees will be moved on to temporary protection visas and also allowed to apply for jobs.

People on temporary protection visas will not be able to reunite with family members abroad while in Australia. And while amendments added to the legislation allow people on these visas to eventually apply for a permanent visa, Mr Morrison has made it clear few, if any, can expect to be granted permanency. Most will remain on temporary visas until it is determined that it is safe to send them home.

Critics say it is a system that traumatises genuine refugees, leaving them stranded without any prospect of certainty or permanence in Australia. They say the temporary protection visa system failed last time – the overwhelming majority of people on them in the Howard years ultimately received permanent protection. This time, they say, the government has loaded the dice by changing the definition of a refugee and introducing a fast-track process that denies an asylum seeker the right to appeal.

Mr Morrison argues that bringing back temporary protection visas allows the government to deal with the 30,000-strong "legacy caseload" of asylum seekers who arrived by boat when Labor was in government and largely haven't been processed. He says the government's stance still sends a message to people smugglers that Australia will not accept their cargo – as before, any new arrivals will still be sent to offshore detention centres.

Why have some senators otherwise opposed to the government's hardline stance on asylum seekers voted for this change?

In part, because 108 children will be removed from detention on Christmas Island and released into the community. Mr Morrison said that process would start last Friday. That people who have been on bridging visas can now look for work has broad support.

Mr Morrison has also promised to increase Australia's refugee intake. Effectively, this just reinstates most of what he had removed. The Coalition cut the intake from 20,000 to 13,750 after being elected. Now he was promising to increase it to 18,750 over the next four years – but only if the legislation was passed.

Critics said these were bribes at best, blackmail at worst. None of the sweeteners were directly tied to the legislation – the increase in refugee intake, for example, is a ministerial promise not mentioned in the bill. Mr Morrison could have taken these steps at any time without legislation.

Has anything not been changed?

The asylum seekers that attempted to reach Australia and were placed in detention on Nauru and Manus Island – including 167 children on Nauru – are not affected. They will remain in those camps until assessed and either resettled someone other than Australia or sent back to their country of origin.

Less clear is what will happen to 25 babies born in Australia to mothers who had been detained on Nauru, but were flown south to give birth. In October, the Federal Circuit Court ruled the government could legally remove the children from Australia. The decision was being appealed in the Federal Court, but that case has no chance of success under the amended laws. Mr Morrison had given an undertaking they would not be removed before last Friday. On Friday, he extended that until January 30. The majority of the babies and their mothers are in Darwin. Five are held at the Melbourne Immigration Transit Accommodation in  Broadmeadows.