Italy's anti-establishment Five Star Movement (M5S) may be on its last legs amid electoral flops, a corruption scandal and an identity crisis that risks tearing it apart, experts say.

In the latest blow, M5S took home just 20% of votes in Sunday's regional election in Basilicata in southern Italy, less than half what it got there in the March 2018 general election.

"What surprises me is not the decline but the fact that it has come so late," Piergiorgio Corbetta, sociology professor at the University of Bologna, told AFP.

"Their growth was unexpected, their fall was inevitable.

"A movement which brandishes the great utopian idea of a fight against all forms of elite, necessarily changes its spots when it becomes elite itself - and that distances some of its voters," he said.

Winning a staggering 32% at the general election last year, things were looking decidedly rosy for a movement founded by a comic and determined to overthrow the old guard in its quest for honest politics.

But it did not have the numbers to govern alone and many of its supporters found it difficult to stomach the decision to form a coalition government with the right-wing, anti-immigrant Northern League.

Its electoral promises have since largely fallen by the wayside as the increasingly popular League calls the shots.

'Free fall'

Having railed against crookedness within traditional parties, M5S has discovered that its biggest victory - taking control of Rome - is proving to be its biggest headache too.

Several prominent members in Rome's mayoral office have been or are currently under investigation and the head of the city council assembly was arrested last week on suspicion of corruption.

On the national level, a growing number of its MPs no longer hesitate to vote against leader Luigi Di Maio and his policies.

The 32-year old is reluctant to expel the rebels, however, according to dissident M5S senator Elena Fattori.

"Perhaps because the Movement is already in free fall. If they start expelling people who support its original theses, they risk disaster" at the European elections in May, she said.

That could be the final blow - should the M5S perform badly in the European Parliament polls it could persuade ambitious League leader Matteo Salvini that the time is ripe to quit the coalition and force a fresh general election.

'Leadership crisis'

Paola Nugnes, another M5S dissident, believes that after eight months of government, "the risk is that there is no longer any difference between the Movement and the League.

"The Movement has in fact 'Salvinised itself', positioning itself ideologically on the right," she said in a reference to Salvini.

And it has paid a heavy price, getting just 19% and 11% respectively in elections in Abruzzo and Sardinia this year - compared to some 40% in both regions last year.

The M5S is suffering a leadership crisis after its charismatic founder, comic Beppe Grillo, took a step back, Corbetta said.

"The Movement is a creature of Beppe Grillo, without him, it would not exist. Grillo is an excellent communicator but not a politician, and that's why he retired," he said.

"It is an orphan. It is experiencing a strong leadership crisis and this dynamic is destined to continue," he added.

Corbetta, who has edited a book of essays on the Movement, said the bad performance at regional elections is proving a turn-off for other voters, creating a vicious circle.

Despite its woes, Di Maio and Salvini have promised each other, and Italians, that the coalition will last its full five-year term.