Former Greek Prime Minister Alexis Tsipras’s leftist Syriza will emerge as the biggest party in next month’s election but without the majority it was hoping for, the first opinion polls since he resigned last week showed yesterday.

One found that almost two thirds of voters felt Tsipras should not have sought a fresh mandate, while both surveys showed that his favoured coalition ally would not make it into Parliament.

That suggested his gamble to call early elections scheduled for September 20 to consolidate his power base could backfire, though in one of the polls over a quarter of voters remained undecided, making the final outcome far from clear.

Syriza was supported by 23 per cent of those polled by ProRata for yesterday’s Efimerida Ton Syntakton newspaper, with New Democracy second on 19.5 per cent.

The previous ProRata poll in early July showed a wider gap in Syriza’s favour, putting the party on 26 per cent compared with 15 per cent for New Democracy.

Syriza would get 29 per cent and the conservative New Democracy party 27.8 per cent if elections were held now, a poll conducted by Metron Analysis for Parapolitika newspaper showed. The result includes undecided voters.

According to the poll, two thirds of voters believe Tsipras is wrong to call an election

Tsipras remained the most popular political leader with 41 per cent of voters having a positive or very positive view, with New Democracy leader Vangelis Meimarakis not far behind with 34 per cent, according to ProRata.

But 64 per cent of Greeks said they believed Tsipras’s move to call snap polls was wrong, while 68 per cent agreed that Greece must stay in the eurozone at any cost, even if that meant further austerity.

“The answers to these two questions lead to the conclusion that early elections may cost the former prime minister and Syriza,” the newspaper said.

The presidency yesterday issued a decree confirming September 20 as the election date.

A caretaker government led by Supreme Court judge Vassiliki Thanou was sworn in earlier yesterday, comprising both technocrats and political figures.

The latter include George Chouliarakis, who was part of Greece’s bailout negotiating team under Syriza, as interim finance minister.

An ally of the former deputy Prime Minister Yannis Dragasakis, Chouliarakis took a decisive role in the talks in the summer and his appointment is likely to be seen as a positive for keeping the country’s bailout programme on track.

“The basic goal is continuity so that precious time is not wasted. There has to be progress on the issue of reinforcing the Greek banking system as quickly as possible,” Chouliarakis said during the handover ceremony.

The head of the council of eurozone finance ministers, Jeroen Dijsselbloem, urged the interim government to continue preparations to implement the bailout during the run-up to the election and said Chouliarakis “knows what he’s doing”.

Nikos Christodoulakis, who served as economy minister from 2001-2004 under the Socialist PASOK government, took the other key portfolio of economy, shipping, tourism and infrastructure.

Tsipras abruptly resigned last week days after clinching an €86 billion bailout package from European and International Monetary Fund lenders, hoping to crush a rebellion by far-left lawmakers and tighten his grip on power.

Popular Unity, the party formed last week by Syriza rebels who oppose the bailout, was backed by 3.5 per cent in the ProRata poll – above the three per cent threshold needed to enter parliament - and 4.1 per cent in the poll by Metron Analysis.

But the Independent Greeks, the ally in Tsipras’s former coalition government, scored roughly two per cent in both polls, meaning Syriza would be forced to seek another coalition partner.

Tsipras this week ruled out cooperating with the main pro-euro opposition parties – New Democracy, the Socialist Pasok and the centrist To Potami. The poll’s result suggested that, in that event, the country would face a second round of elections.

Still, with Syriza’s move to accept the EU/IMF bailout, the next parliament will continue to have a substantial majority of pro-bailout parties, meaning the country’s future in the eurozone looks more secure than it did at the start of the year.

One third of those who supported Tsipras’s party in the January 2015 elections that took him into office said they were unsure if they will do so again, the ProRata poll said.

It also showed 25.5 per cent of voters were still undecided, making them the biggest bloc.