One of Australia’s top pollsters has dismissed the importance of Malcolm Turnbull and Bill Shorten’s personal approval ratings as polls show the Opposition Leader taking a hammering as preferred prime minister.

Amid the government’s strategy to attack Mr Shorten, Malcolm Turnbull has notched up a commanding lead in the preferred PM stakes in the two major polls, Newspoll and Fairfax-Ipsos, despite Labor retaining a comfortable two-party preferred advantage.

On Monday, Labor MPs were forced to defend Mr Shorten after the latest Fairfax-Ipsos poll showed his approval rating had fallen from 42 to 36 per cent and that he now was trailing by 17 percentage points as preferred PM.

But Gary Morgan, the executive director of Roy Morgan Research, said that measure would have almost no bearing on the next election.

“I’ll tell you one thing. Don’t worry about preferred PM or leadership approval ratings. [Helen] Clark in New Zealand, [Ronald] Reagan, [Margaret] Thatcher, they all had poor approval ratings. It’s rubbish. People don’t vote for that reason. They vote for what will make their lives better,” he said.

“The underlying issues are to do with people and their families. The politicians ranting and raving about the leaders, the public don’t care about that. No one gives a damn. What they’re interested in is what’s going to happen to them.”

The deterioration in the Opposition Leader’s personal standing among voters comes as the government adopts a “Kill Bill” strategy, by focusing on Mr Shorten as untrustworthy and a threat to the economy and power prices.

Pollster Gary Morgan says the voting public don’t care about the ranting and raving of leaders.

Despite being in the polling business, Mr Morgan said he “wouldn’t be taking too much notice of the public opinion polls” and that he did not “assume the polls are right”.

“They were all wrong on Brexit and they were wrong on Donald Trump so I don’t know why the media gives so much prominence to them,” he said.

Mr Morgan’s comments may seem unusual coming from a pollster. Roy Morgan Research does not conduct a regular federal poll in Australia like Newspoll or Ipsos, though it is undertaking voter intention polls for the upcoming New Zealand election.

Labor has created a sustained lead over the government, winning 19 Newspolls in row, and most commentators believe the opposition is in the box seat to win the next election.

But Mr Morgan warned the party’s focus on tax, including its crackdown on family trusts and plans to reintroduce the debt levy on the nation’s top earners, could prove costly at an election.

“You win elections by saying you’re going to lower taxes not raise them,” he said.

“I think they’ve got very little chance of winning the election if they maintain they are going to put up taxes.”

Mr Morgan also predicted that minor parties such as the Nick Xenophon Team and One Nation would benefit from unprecedented dissatisfaction among the electorate.

“I think voters are fed up with politicians,” he said.

“If they (the major parties) haven’t got the message yet they’ll get it at the next election when the minority parties have a massive majority in the Senate.

“There’s a large number of people undecided and a large number of people who will support the minor parties. What we said before the last election, that the minor parties would control the Senate, was completely right.”

Asked to name the issues that will be on voters’ minds at the next election, Mr Morgan said: “Anything that affects the family will be important. The cost of food, the cost of power.”

He said the “biggest thing affecting the country today” was “true unemployment and underemployment”.