Turkey’s parliament has begun debating a controversial new draft constitution aimed at expanding the powers of the presidency under Recep Tayyip Erdoğan.

The new constitution, which is expected to be put to a referendum by the spring, would replace the basic law drawn up in 1982 after Turkey’s military coup. It seeks to establish for the first time a presidential system for ruling the modern republic created from the ashes of the Ottoman empire.

Critics have claimed the move is part of a power grab by Erdoğan – Turkey’s prime minister from 2003 to 2014, and president ever since – for one-man rule in the wake of a failed coup in July.

But Erdoğan and the ruling Justice and Development party (AKP) say the presidential system would bring Turkey into line with countries such as France and the United States and is needed for efficient government.

The debates on the 18-article new constitution began after the draft was agreed by a parliamentary commission. The two readings are expected to last between 13 and 15 days.

There were protests from some quarters as parliament began its deliberations.

According to the private Doğan news agency, Selahattin Demirtaş, the jailed co-leader of the Peoples’ Democratic party, said the arrest of 11 members of the party for alleged ties to the outlawed Kurdistan Workers party (PKK) had stripped them of their chance to challenge the draft constitution and “makes the debate and the vote controversial from the very start”.

A rally outside the parliament building in Ankara against the change descended into violence after riot police used teargas and pepper spray on the demonstrators. Police also fired water cannons to disperse protesters, pushing back with their shields those who returned to the fray.

“We don’t want a system where only one man leads,” demonstrator Abdullah Sundal told Agence France-Presse TV, adding that protestors will do everything they can to stop the draft becoming law.

The AKP needs more than 330 votes - a three-fifths majority - for the bill to be submitted to a referendum for voters’ approval.

However, the November 2015 election left the AKP short of a super majority in parliament and it is relying on the support of the opposition rightwing Nationalist Movement party, the fourth largest in the legislature.

The new constitution is opposed by the biggest opposition party, the Republican People’s party (CHP), whose deputy chairman Bülent Tezcan said it would restore powers “to the palace”, where they were taken away from the Ottoman Sultan a century ago.

“There’ll be no censure motions, no vote of confidence, no parliamentary inquiries,” fellow CHP lawmaker Deniz Baykal warned.

But on Monday, AKP’s parliamentary group deputy chairman Mustafa Elitaş said he was expecting at least 20 deputies from the opposition CHP to cross the aisle to vote with the government.

If the measure is approved by parliament, a referendum is expected to take place within 60 days, indicating a date in late March or early April.

Pro-government newspapers have predicted a thumping victory for the ruling party although other commentators have been more cautious about the results of a plebiscite.

AKP politician İbrahim Halil Fırat, who helped draw up the proposed new constitution, said it would make clear the roles of government and president and ensure “stability”.

The proposed constitution is expected to lead to the creation of the posts of vice presidents and the abolition of the office of prime minister.

There would no longer be a formal cabinet but there would be ministers, whom the president would have the power to appoint and fire.

The president would be elected for a five-year term and serve for a maximum of two mandates.

If Erdoğan’s existing time as president is not counted, it would mean in theory he could stay in office until 2029.

Parliamentary elections would be held every five years – not four as at present – and on the same day as presidential polls.

Both elections would be scheduled to take place on 3 November 2019.

Along with a slew of terror attacks, the political uncertainty has been one of the factors pressuring the Turkish lira, which has lost 18% in value against the dollar over the last three months.

The currency slumped to a new record low on Monday, a situation LCG senior market analyst Ipek Özkardeşkaya described as “alarming”.

She warned the upcoming constitution referendum “could push the country toward a greater chaos and further weigh on its currency”.