Image copyrightADEM ALTAN/AFP/GETTY IMAGES

A new draft constitution that would significantly increase the powers of Turkish President Recep Tayyip Erdogan has been put to a referendum. Here, the BBC's Turkey correspondent, Mark Lowen, explains why opponents of the bill have fought it every step of the way.

In one brawl, a government MP alleged an opponent bit into his leg. In another, a plant pot was hurled across parliament. A microphone was stolen and used as a weapon. An independent MP handcuffed herself to a lectern, sparking another scuffle. The parliamentary debate on changing Turkey's constitution wasn't a mild affair.

On the surface, it might seem a proposal that would enjoy cross-party consensus: modernising Turkey's constitution that was drawn up at the behest of the once-omnipotent military after the coup of 1980.

But instead it's arguably the most controversial political change in a generation, becoming in effect a referendum on the country's powerful but divisive President Erdogan.

The plan would turn Turkey from a parliamentary to a presidential republic. Among the numerous changes:

• The role of prime minister would be scrapped. The new post of vice president, possibly two or three, would be created.
• The president would become the head of the executive, as well as the head of state, and retain ties to a political party.
• He or she would be given sweeping new powers to appoint ministers, prepare the budget, choose the majority of senior judges and enact certain laws by decree.
• The president alone would be able to announce a state of emergency and dismiss parliament.
• Parliament would lose its right to scrutinise ministers or propose an enquiry. However, it would be able to begin impeachment proceedings or investigate the president with a majority vote by MPs. Putting the president on trial would require a two-thirds majority.
• The number of MPs would increase from 550 to 600.
• Presidential and parliamentary elections would be held on the same day every five years. The president would be limited to two terms.

The government - and, principally, President Erdogan - argue that the reforms would streamline decision-making and avoid the unwieldy parliamentary coalitions that have hamstrung Turkey in the past.

Since the president is no longer chosen by parliament but now elected directly by the people, goes the argument, he or she should not have to contend with another elected leader (the prime minister) to enact laws.

The current system is, they say, holding back Turkey's progress. They even argue that the change could somehow end the extremist attacks that have killed more than 500 people in the past 18 months.

Image copyrightOZAN KOSE/AFP/GETTY IMAGESImage captionHundreds of people have been killed in attacks in Turkey in the past 18 months

A presidential system is all very well in a country with proper checks and balances like the United States, retort critics, where an independent judiciary has shown itself willing to stand up to Donald Trump and a rigorous free press calls him out on contentious policies.

But in Turkey, where judicial independence has plummeted and which now ranks 151 of 180 countries in the press freedom index of the watchdog Reporters Without Borders, an all-powerful president would spell the death knell of democracy, they say.

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Mr Erdogan's opponents already decry his slide to authoritarianism, presiding over the world's biggest jailer of journalists and a country where some 140,000 people have been arrested, dismissed or suspended since the failed coup last year. Granting him virtually unfettered powers, says the main opposition CHP, would "entrench dictatorship".

"The jury is out," says Ahmet Kasim Han, a political scientist from Kadir Has University. "It doesn't look as bad as the opposition paints it and it's definitely not as benevolent as the government depicts it. The real weakness is that in its hurry to pass the reform, the government hasn't really explained the 2,000 laws that would change. So it doesn't look bright, especially with this government's track record."

Image copyrightBURAK KARA/GETTY IMAGESImage captionSince the failed coup 140,000 people have been arrested, dismissed or suspended from their jobs

The governing AK Party had to rely on parliamentary votes from the far-right MHP to lead the country to a referendum. For long, the MHP leader, Devlet Bahceli, opposed the presidential system: "The Turkish nation has never allowed a Hitler," he once said, "and it will not allow Erdogan to get away with this," calling it the recipe for "a sultanate without a throne".

But arm-twisting and rumours that he could be offered one of the vice presidential posts has prompted a spectacular U-turn. The question now is whether he can persuade his party to follow. The party's deputy chairman and several local MHP officials have already resigned over Mr Bahceli's stance.

"It seems this is not going Bahceli's way," says Dr Kasim Han. "But the naysayers may not feel able to go against the party culture by contradicting the leader."

Opposition to the reform is led by the centre-left CHP and the pro-Kurdish HDP parties, the latter of which has been portrayed by the government as linked to terrorism. Several of its MPs and the party leaders are now in prison.

Image copyrightADEM ALTAN/AFP/GETTY IMAGESImage captionDevlet Bahceli, leader of the far right MHP, now supports the proposed constitutional changes

AKP and MHP voters who oppose the reform may feel pressured into voting in favour, so as not to be tarnished as supporting "terrorists", especially since the referendum will take place under the state of emergency imposed after the attempted coup.

"Holding the vote under this state of emergency makes it susceptible to allegations that people don't feel free to say no," says Dr Kasim Han. "It casts a shadow over the outcome."

Polling has been contradictory and Turkish opinion pollsters are notoriously politicised. But all signs point to a very tight race.

With the detail of the constitutional reform impenetrable to many, the referendum has become focused around Mr Erdogan himself: a president who elicits utmost reverence from one side of the country and intense hatred from the other.

The decision as to whether to grant him the powers he's long coveted will determine the political fate of this deeply troubled but hugely important country.