ROME (Reuters) - Italy’s anti-establishment 5-Star Movement, which leads most opinion polls ahead of a national election due by May next year, on Friday launched an internal ballot to choose its leader and candidate for prime minister.

FILE PHOTO: Luigi Di Maio of the 5-Star Movement looks on as he attends a news conference in Rome, Italy March 23, 2017. REUTERS/Alessandro Bianchi

The hot favorite is 31-year-old lower house deputy Luigi Di Maio, the party’s most high-profile and popular politician, who has made no secret of wanting the job and appears to have no rivals to worry him.

The biggest problem for the maverick movement founded eight years ago may be finding credible alternative candidates in the contest, which will take the form of an online vote of 5-Star’s members, in line with its credo of direct democracy.

Di Maio, who is deputy speaker of the Chamber of Deputies, is considered a good communicator and one of 5-Star’s more moderate figures.

A post on 5-Star’s official mouthpiece, the blog of its founder Beppe Grillo, said the candidate for prime minister would also be the party’s leader, something which is not always the case in Italian politics.

Grillo, who founded 5-Star in 2009, has so far acted as its de facto chief, though he has never run for any office and the party has always prided itself as having a horizontal structure with no official leader.

The only person considered a realistic threat to Di Maio, the fiery deputy Alessandro Di Battista, has given no indication that he plans to run.

Another deputy seen as a potential challenger, Roberto Fico, who represents the left wing of the party and has recently distanced himself from Di Maio’s tough positions on law-and-order and immigration, has also not yet made any move.

The post on Grillo’s blog said 5-Star’s local and national representatives who wish to run had until Monday to present their candidacies.

The timing of the online vote has not yet been set but the winner is due to be announced on Sept 23 at 5-Star’s annual national meeting at the Adriatic coastal town of Rimini.