A celebrated sailor turned MP for Italy’s governing Five Star Movement (M5S) has been given an ultimatum by party leaders to get back to work or resign after it emerged he has spent the majority of his time since winning election in early March on his boat.

Andrea Mura, the winner of several sailing regattas, secured his seat in parliament representing Cagliari, Sardinia, after defeating the island’s former governor and Forza Italia politician, Ugo Cappellacci.

But instead of fulfilling his political duties, as promised in a blogpost after his victory, he has been absent for 96% of the time.

Amid outrage from opponents, M5S leaders were forced to issue a note telling the sailor to commit himself to his voters or quit.

“If the deputy of the Five Star Movement wants to continue to dedicate himself to other activities, neglecting the cabinet mandate given to him by citizens, he has only one path to take: present his resignation to parliament,” wrote Francesco D’Uva and Stefano Patuanelli, M5S group leaders in the lower and upper chambers of the Italian parliament.

Andrea Mura off Plymouth, Devon, in May 2017. Photograph: Alamy

Mura defended the amount of time spent sailing, saying he had always maintained that his role would be “to defend the ocean” more than that of a parliamentarian.

“Political activity does not only take place in parliament, it can also happen on a boat,” he told the Sardinian newspaper Unione Sarda.

But his high rate of absenteeism is an embarrassment for a party that prides itself on its dedication to its citizens and its honesty.

The M5S leader, Luigi Di Maio, pledged to rid Italian politics of the old guard during the election campaign, saying his team would be made up of people who could improve the country.

Di Maio, Italy’s deputy prime minister and minister of labour, in coalition with the far-right League, had said he considered Mura, 53, to be one of those people. “I am convinced that Andrea will put his heart and mind into the job of being in parliament,” he said after the election.

The party has also long railed against high politicians’ salaries, although Di Maio came under attack last week for hiring an inexperienced secretary – a friend from his home town – on €72,000 (£64,000) a year on the basis of her “honesty”.

Cappellacci, Mura’s defeated rival, led the outcry over Mura’s absenteeism. “While ordinary citizens go to work to receive a salary, for Mura the logic of being paid by the state in return for going to parliament is a moral discussion,” he said.

At the time of his election, Mura said he would take on the role of representing Italy with passion. In 2017, he won the Ostar race, one of the toughest solo competitions, which starts in Plymouth in the UK and ends in Newport, Rhode Island.