Malcolm Turnbull’s approval rating has continued to slide, reaching its lowest level since he took over as prime minister, according to the latest Essential poll.

The poll of 1,000 respondents, released on Tuesday, showed that Turnbull’s net approval rating fell from -8 in November to -12 in the poll, taken from Friday to Monday.

A total of 46% of voters disapproved of Turnbull, compared with 34% who approved of his performance.

Of those polled 35% approved of the performance of the opposition leader, Bill Shorten, and 38% disapproved. His net approval rating lifted from -9 in November to -3 in December.

But Turnbull maintained his lead as preferred prime minister, leading 39% to Shorten’s 28%. Labor led 53-47 in two-party preferred terms.

More respondents said the Liberal party was becoming more conservative (37%) than said it was becoming more progressive (14%), a dramatic reversal from when the question was last asked in December 2015 and fewer voters thought it was becoming conservative (24%) than progressive (27%).

The poll came after a week in which the environment minister, Josh Frydenberg, first left an emissions intensity scheme on the table then backtracked and ruled it out, in a move critics said left the Turnbull government without a credible replacement for its policy to pay polluters to lower emissions.

Respondents were evenly split on whether Labor was becoming more conservative or more progressive, with 21% agreeing with each option.

Asked if a new conservative party was formed and included people such as former prime minister Tony Abbott, 23% of people said they were likely to vote for such a party compared with 58% who said they were unlikely to. That was a small increase from December 2015 when just 20% wanted the more conservative option.

In July the South Australian senator Cory Bernardi formed an Australian Conservatives movement but said he had done so to make the Liberal party stronger.

Support for a conservative party was highest among Coalition voters, 41% of whom said they were likely to vote for it, followed by those who voted for other parties, 25% of whom said the same.

Asked about ways to increase wages of Australian workers, the most popular options were increasing the minimum wage (80% support) and cutting personal income taxes (71%).

People favoured cutting company tax “so that businesses invest and give workers pay rises”, with 61% in favour and 24% opposed.

Not as many wanted to give more power to unions to negotiate pay rises, with 43% in favour and 41% opposed.

In late November the government passed the Australian Building and Construction Commission bill, which unions said would weaken their collective bargaining rights.

Turnbull and the employment minister, Michaelia Cash, said the tougher building regulator would be a boon to the 1m employees of the construction sector despite Turnbull suggesting in the election campaign it would help stop “excessive” pay rises in the sector.