His resignation immediately drew a withering attack from Liberal senate leader George Brandis, who said he had broken faith with Liberal voters for defecting and he "will have to account to the Australian people and to his own conscience".

The former Liberal senator, who was verbally carpet bombed by furious ex-colleagues on Tuesday, made a statement about his move – which has delivered another hit to the fortunes of Malcolm Turnbull's ailing government – to the Senate chamber on Tuesday.

"This has been a very difficult decision for me, perhaps the most decision of my political life. I stand here today, both reluctant and relieved," he said, announcing his resignation.

"The body public is failing the people of Australia. It is clear that we need to find a better way. The level of public disenchantment with the major parties, the lack of confidence in our political process and the concern about the direction of our nation is very, very strong."

Senator Bernardi said the "respect for the values and principles that have served us well seem to have been set aside for expedient, self-serving, short-term ends".

"I have spoken of the need to restore faith in our political system and to put principle back into politics. I regret that too often these warnings have been ignored by those who perhaps needed to hear them most. It really is time for a better way. For a conservative way."

"Today I begin something new, built on enduring values and principles that have served our nation so well for so long. It is a political movement of Australian Conservatives.

He pledged a political movement that would help create stronger families, limit the size and scope and reach of government and rebuild confidence in civil society – but with little detail about how those aims would be delivered.

Senator Brandis said that in the seven months since the federal election "nothing has changed. There is no policy for which the Liberal Party and the government stands today, which is not the same as the platform on which Senator Bernardi sought election by the people of SA only seven months ago".

"What Senator Bernardi has done today is not a conservative thing to do because breaking faith with the electorate, breaking faith with the people who voted for you, breaking faith with the people who have supported you through thick and thin for years."

Labor senate leader Penny Wong said the defection underlined just how divided the Coalition was under Mr Turnbull, and that the Prime Minister was "leading a government that doesn't have an agenda, that doesn't have a philosophical framework".

Senator Bernardi's defection had been in the offing for years, though he had previously indicated a desire to work for change from within the Liberal Party.

Cabinet ministers Peter Dutton, Barnaby Joyce, Steve Ciobo and Christopher Pyne led the criticism of Senator Bernardi, with Mr Dutton labelling it a "betrayal" and Mr Ciobo pointing out he had spent more time criticising his own colleagues than Labor.

When he spoke to the Prime Minister on Tuesday morning, Senator Bernardi said to Mr Turnbull that he was quitting, in part, because of the removal of Tony Abbott in 2015, while also warning there were discussions underway to remove Mr Turnbull.

Mr Turnbull, in turn, is said to have asked Senator Bernardi how he could justify leaving the Liberal Party just seven months after he was elected on the party's ticket - a question the turncoat could not answer.

The South Australian received just 2043 first preference votes as the second candidate on the Liberal Party ticket at the 2016 election, or 0.025 per cent of a quota.

In comparison, the Liberal Party received 345,767 votes, underscoring the point made by angry Liberals that the vast majority of voters cast their preference for a party, not an individual in the Senate.

Former prime minister Tony Abbott said Senator Bernardi "has made an important contribution to our public life and I deeply regret his decision to leave the Liberal Party".

In an apparent reference to Mr Turnbull's leadership, Mr Abbott added: "while Cory and I have sometimes disagreed I'm disappointed that more effort has not been made to keep our party united".

WA MP Andrew Hastie said Senator Bernardi was a friend but "I wish that he had attended the Liberal Party room meeting this morning, looked us all in the eye and explained his reasons".