More than 20% of the Australian electorate intends to vote for the Greens or a minor party, and another 7.2% remain undecided, despite Malcolm Turnbull’s pleas for voters to shun minor parties in the interest of “stable government” and avoiding “chaos”, according to a new poll.

With just one week until polling day, the Coalition leads the two-party preferred vote in the Seven ReachTel poll 51% to 49%, unchanged from the previous week.

The poll also looked at the New South Wales electorate of Cowper, where the independent candidate Rob Oakeshott is making a late bid to unseat the sitting Nationals MP Luke Hartsuyker, and found the result in the balance – each candidate is on 50% of the two-party preferred vote.

After a penultimate week of campaigning dominated by scare campaigns, 11.5% of voters say they intend to vote for “others” – including the Nick Xenophon Team – and 9.2% say they will vote for the Greens. When the 7.2% who said they remained undecided were pressed to indicate a preference, the “others” vote rose to 13.3%.

Liberal strategists believe the international economic uncertainty flowing from Britain’s shock “Brexit” vote to leave the European Union will underscore Turnbull’s message that Australians should opt for the “stability” of a majority Coalition government.

But Labor sources say the disengaged and volatile electorate means the election is still a contest and their “people first” message is also appealing to voters worried about who would be looked after in an economic crisis. They also point to Labor’s record in steering the Australian economy through the global financial turmoil in 2008.

Turnbull reassured Australians there was “no cause for alarm” because of the British vote, but also said it bolstered his electoral pitch.

“These are the global headwinds of which I’ve often spoken. We need strong majority government. Strong Coalition leadership. We need a strong economic plan. We have that. We’ve set that out. We’ve set out our plan that will deliver, and is delivering today, economic growth and stronger employment,” he said.

The opposition leader, Bill Shorten, said Brexit wouldn’t change Australia’s “economic fundamentals” but showed the need for “inclusive growth” to avoid voter disenchantment.

The poll showed that economic management had risen as an issue nominated by voters as highly influential in their voting decision. A total of 29.9% said it was an issue that would “influence their decision most” compared with 23.8% three weeks ago.