Matteo Salvini’s political fortunes have been given a boost after an exit poll by Italy’s state broadcaster pointed to a win for a rightwing coalition backed by his League party in a regional election in Umbria.

Donatella Tesei, backed by the League, the far-right Brothers of Italy and former prime minister Silvio Berlusconi’s Forza Italia, will be elected governor with 56.5% to 60.5% of the vote, according to an exit poll for state broadcaster RAI.

The vote in the traditional centre-left stronghold, which has a population of less than 900,000, restores impetus to Salvini after his political blunder that saw the League lose power nationally this summer.

The hard-right leader walked out of government with the anti-establishment 5-Star Movement in August, expecting to trigger a national election that polls predicted he would win. Instead, 5-Star struck a deal with the centre-left Democratic party (PD), shunting Salvini into opposition.

However the initial indications from Umbria suggest the new 5-Star/PD alliance has failed its first electoral test.

The exit poll suggested Vincenzo Bianconi, leader of a civic alliance backed by 5-Star and the PD, would get 35.5% to 39.5%, while Claudio Ricci, a rightwing independent candidate, is seen at 1.5% to 4.5%.

The League chief had criss-crossed landlocked Umbria for weeks, promoting his national pledge to introduce a flat-tax rate many economists say Italy cannot afford, but which the League insists is needed to revive the sluggish economy.

His message found fertile ground in Umbria, where output slumped 15% in the decade after the 2007 financial crisis, compared with a 5% slide across Italy, according to Bank of Italy data.

Umbria marks the eighth straight victory for the centre-right in regional ballots since the last national election, in March 2018.

More important tests lie ahead that could potentially undermine the new national government.

In December, the poor southern region of Calabria goes to the polls and it will be the turn on 26 January of Emilia Romagna, a northern region with more than four times the population of Umbria and which is the historic heartland of Italy’s left.

Opinion polls show the League, with its anti-migrant, anti-tax message, has shed little support since it lost power nationally and remains easily Italy’s most popular party, with around 30% of the vote.