This article is more than 2 years old

This article is more than 2 years old

Labor has increased its lead against the Coalition in Newspoll to 52% to 48% in two-party-preferred terms, despite a fall in popularity for Bill Shorten and majority support for the government’s company tax cut package.

The Newspoll, released on Monday, found that 63% of voters support a 25% rate of company tax ahead of a two-month campaign for five Super Saturday byelections on 28 July, in which Labor is running hard against the government’s plan to extend that lower rate to larger companies.

At Labor’s Victorian state conference on Sunday Shorten warned that the only way to stop corporate tax cuts was to elect Labor federally. He used factional backing from the Australian Workers’ Union and the Construction Forestry Mining Maritime and Energy Union to shut down debate about imposing a time limit on offshore detention of refugees and asylum seekers.

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The five byelections, scheduled for the last day of Labor’s national conference, which will now be rescheduled, come at a critical time for Shorten. The opposition leader’s personal popularity lags behind Malcolm Turnbull.

The Newspoll found that Turnbull ­had extended his lead as the preferred prime minister, up a point to lead 47% to Shorten’s 30%, down two points and reaching one of his lowest levels since the 2016 election.

The poll was the 66th straight poll in which Shorten has recorded a negative approval rating, although among Labor voters Shorten enjoyed 39% support as preferred Labor leader compared with Anthony Albanese on 22%.

Among all voters Albanese is the preferred Labor leader, with 26% support compared with 23% support for Shorten and his deputy, Tanya Plibersek.

The Coalition lost one point in primary support, down to 38%, while One Nation increased its vote by two points. The latest Guardian Essential poll and the previous two Newspolls had the Coalition trailing 49% to Labor’s 51% in two-party-preferred terms.

Labor is campaigning against the government’s plan to cut the corporate tax rate to 25% for companies earning more than $50m a year but is wary of signs that the Coalition may drop the package.

On Sunday Shorten told the Victorian Labor conference he was “damn sure Australians do not want to give a $17bn tax cut to the big banks”. It was a matter of “when, not if” the government dumped the corporate tax cut policy.

But in preparation for a shift in Coalition policy, the opposition leader warned that the only way to ensure the policy never returned was to elect Labor. “If you want to see the corporate tax plan dead, buried, and cremated, do not believe what the investment banker and those who sit opposite tell us,” he said.

“Because you know that if they ever control the Senate, that corporate tax plan, that rotten scheme, will be right back on the agenda.”

Campaigning for the five byelections is in full swing, with Shorten to visit a GP super clinic in Devonport with Labor’s candidate for Braddon, Justine Keay, on Monday.

Turnbull, Shorten and the quest for the winning message | Katharine Murphy Read more

Despite Labor fury at the 79-day delay before the byelections, the timeline will allow Shorten to put off damaging internal debates at the party’s national conference over asylum seeker policy.

On Sunday Shorten said he was “very committed to making sure the boats don’t start again”. “The current government would like to say that there’ll be another policy; there won’t be,” he said. “We also just happen to think that we shouldn’t be leaving people in semi-indefinite detention for five years just to achieve this.”

Labor for Refugees activists and delegates were outraged by the decision to postpone their plan to impose a 90-day time limit on offshore detention, as the motion was referred to committee. The CFMMEU Victorian secretary John Setka defended the decision as “democracy at work” on the conference floor.

On Monday Victoria’s premier, Daniel Andrews, told Radio National it was “not unusual” for motions to be referred to committee and the immigration policy would be discussed at the national conference.