Updated 1.15pm - Added PN remarks

Godfrey Farrugia has resigned as Labour Party whip.

In an open letter to Prime Minister Joseph Muscat, Dr Farrugia said that Labour Party ideals had been betrayed to push forward the agenda of "the few who do not have the national interest at heart."

Dr Farrugia said that he would be staying on as a PL MP, in an attempt to push for change from within the party.

"I thought it through at great length," Dr Farrugia wrote in his open letter, "I voted as whip even when I was asked to vote against my own conscience."

WATCH: Farrugia suggests Konrad Mizzi should resign

Dr Farrugia said that he remained convinced that the PL could "change the country's direction around" in the final year of its legislature. "To do this, the government must assume a form that will see it regain lost credibility," he wrote.

"I hope I can help bring the party leadership to its senses so it can stop using the people to protect its power," he added.

Dr Farrugia said that despite various successes, party leadership had "lacked maturity."

"Of course I never expected us to be perfect. But justifying mistakes and calling what is wrong, right, is another story," he wrote.

Dr Farrugia, who served as an independent mayor of Żebbuġ in the 1990s and contested the general elections for the first time in 2013 on a PL ticket, noted that instead of reforming authorities to ensure they were kept at arms' length from political control, "we did the opposite."

"We strengthened political control when the situation required us to apply division of power principles. We lost our moral fibre."

Last year, Dr Farrugia had made it clear that he had severe reservations about the way in which the government handled fallout from the Panama Papers scandal.

"If I were Minister [Konrad] Mizzi, I would have resigned," he had told Times of Malta outside parliament.

The Labour MP was conspicuous by his absence during the PL's Labour Day festivities last year, and pointedly declined to comment ahead of a parliamentary vote of no confidence in Dr Mizzi.

In a statement, the Labour Party said Dr Muscat had received Dr Farrugia's letter of resignation and thanked him for his work.

Labour MP Tony Agius Decelis will be acting whip until a replacement for Dr Farrugia is elected.

'This is a battle between right and wrong' - de Marco

In a press conference held this afternoon, Nationalist Party deputy leader Mario de Marco said Dr Farrugia's resignation letter was significant because it unmasked the deception behind the PL movement built by Joseph Muscat.

"The hopes and dreams of the well-intentioned people within this movement never came to fruition because its leaders, we now know, had different plans," Dr de Marco said.

"This is not a battle between Nationalists and Labourites, but rather one between the well-intentioned and those who snatched the country for their own gains, between right and wrong."

Malta desperately needed people to unite behind a national force, Dr de Marco said, as he paid tribute to Dr Farrugia for having spoken out.