His energetic stint at the helm of Italy’s government was brought to a juddering halt when, in 2016, he was effectively sacked by voters after suffering an embarrassing defeat in a constitutional referendum. Now Matteo Renzi is back, casting himself as the man to save Italy from the potential grip of a far-right government led by the League’s Matteo Salvini and calling on all “responsible politicians” to back him to thwart the extremist threat. He is re-entering the fray, he insists, for the sake of the country’s future – and not to reignite his own career.

“For my personal rating and consensus it would be better to stay silent,” Renzi told the Observer in an exclusive interview last week. “But Salvini must be stopped, and it’s important to give a strong message – there is an alternative.”

Italy, no stranger to political turmoil, has once again been plunged into uncertainty after Salvini, deputy prime minister and leader of the League, announced on 8 August that he was ending his party’s stormy relationship with the anti-establishment Five Star Movement (M5S), saying it was unworkable due to the incessant quarrelling over policies. Seeking to exploit the League’s growing popularity, Salvini called for snap elections and immediately declared himself a candidate for prime minister, urging supporters to give the League “the strength to take this country in hand and save it”. He took to the campaign trail on the beach, DJ-ing topless and then Instagramming selfies afterwards.

But he hadn’t counted on Renzi scheming to derail him. Renzi, a senator, is spearheading talks between factions of the Democratic party (PD) and the M5S, a longtime foe, with the idea of carving out a new majority that could see the government through the delicate autumn budget period, and possibly longer. At first, the idea seemed unthinkable, with the leader of Renzi’s centre-left PD, Nicola Zingaretti, describing it as “a gift to the dangerous right” and his M5S counterpart, Luigi Di Maio, saying he would never “sit at the table with Renzi”.

But, since Tuesday, when both parties caught Salvini off-guard by voting against the League’s motion to inflict a vote of no-confidence on prime minister Giuseppe Conte, the proposal has looked more plausible. Conte will address the political crisis in parliament on Tuesday and may face a confidence vote.

We did a lot of reforms, made a lot of difference. OK, we lost the referendum but I am happy about the service we gave Matteo Renzi

Renzi told the Observer that Salvini was weaker since Tuesday: “For the first time there was a message against his propaganda.” He urged politicians from the PD and M5S to cast aside their egos and make a “strong response” to a perilous quest for power by Salvini that could create Europe’s first fully far-right government. The League is polling at about 38% and could team up with Brothers of Italy, a party with a neofascist lineage, to guarantee a majority in the event of snap elections.

“The idea of making an agreement with a movement that has attacked me for five years and used fake news against me and my family is difficult to accept, but for the future of your country, you have to put your emotions aside,” Renzi said, referring to the PD’s and the M5S’s years of animosity. “I ask every responsible politician to please, please block this unbelievable [plan] to go to elections. My dream is to help my country avoid the destruction of its economy and institutions, not be the guy who holds the keys to create a government.”

A return to the centre stage of Italian politics would be quite a turnaround for a man who crashed out spectacularly two and a half years ago. Renzi had intended the referendum on constitutional reform to lead to an ambitious revamp of the political system, with the aim of making it more stable and efficient. Instead, by promising to quit if he lost the vote, it led only to his own departure from Palazzo Chigi, the prime minister’s residence in Rome, and helped lay the foundations on which the League and M5S prospered.

Facebook Twitter Pinterest Matteo Salvini meets supporters at the beach in the Sicilian town of Taormina. Photograph: Antonio Parrinello/Reuters

He had stormed to power in February 2014, nicknamed “Il Rottamatore” – the Demolition Man, and managed to revive the floundering PD, leading it to over 40% in the European elections that May. He quickly moved to undertake labour market reforms while restoring Italy’s reputation in Brussels. But Renzi made a fateful miscalculation of his popularity during the referendum campaign and became the architect of his own demolition. He remained at the helm of a deeply divided PD until its dismal performance in the March 2018 elections. “Instability is the key word for Italian politics, for three years I tried to change this,” he said. “We did a lot of reforms and made a lot of difference. OK, we lost the referendum and for sure, made mistakes, especially me. But I am happy about the service we gave.

After more than a week of twists and turns and rampant speculation, how things will play out on Tuesday is anyone’s guess. If Conte’s address leads to a confidence vote, it might not take place on that day. He could choose to resign, avoiding the vote. There is also the prospect of Salvini resigning and withdrawing his ministers. The power to dissolve parliament rests with president Sergio Mattarella, who could seek an alternative majority or call an election. If he chooses the latter, then an election would need to take place within 45 to 70 days. The last time Italians voted in the autumn was in 1919, preceding fascist dictator Benito Mussolini’s acquisition of power in 1922.

Renzi believes EU’s fourth-largest economy would go into recession and suffer a VAT rise to 25% if a vote is held so soon. On top of this, a no-deal Brexit in October and Germany’s sluggish economy would compound things in Europe as a whole. Blocking the eurosceptic Salvini could also be Italy’s chance “to return to the political game” in Brussels, Renzi said.

There are vast differences between the PD and M5S but the main impediment to them striking a deal is Renzi himself. An accord would need the full support of Zingaretti, who told the Guardian in May that he wouldn’t work with a party sullied by the League. In the middle of last week, he was reportedly warming to the idea, but by Friday denied having any interest in a “patch-up” government, adding the PD is ready for elections.

Meanwhile, rumours on Friday that a damaged Salvini was seeking to patch things up with the M5S, offering Di Maio the premiership, were blasted by M5S as “fake news”.

Renzi may have more followers than Salvini on Twitter, and still wields significant influence within the PD, but there is no denying that his popularity was severely dented by the failed referendum. Many Italians balk at the prospect of him being back at the forefront of politics. He is banking, though, that they will balk more at the prospect of prime minister Salvini. “Salvini is weaker, and this showed on Tuesday: for the first time there was a message against his propaganda,” he said. “If the League won with fake news and propaganda, it will lose with reality and politics.”

• This article was amended on 19 August 2019 to clarify that Mussolini came to power in 1922 not 1919.