The independent candidate Rob Oakeshott could be on the verge of a last-minute upset win in the battle for the seat of Cowper, according to a ReachTEL poll.

The poll of 842 Cowper residents, released on Wednesday, showed sitting Nationals MP Luke Hartsuyker on a primary vote of 39.4%, compared with 24.8% for Oakeshott, 13.2% for Labor and 8.2% for the Greens.

In the 2013 election Hartsuyker won 53% of the primary vote and 61.7% of the two-party preferred vote.

Although Oakeshott is behind Hartsuyker and there are no two-party preferred results released with the poll, commissioned by GetUp, Hartsuyker’s primary vote falling below 40% leaves him vulnerable if Oakeshott can garner preferences from other candidates.

Oakeshott announced his decision to contest Cowper on Friday, after quitting parliament in 2013 when he represented the neighbouring seat of Lyne. He had retired citing “exhaustion” after the hung parliament in which his vote was critical to propping up the Gillard government.

Oakeshott told Guardian Australia his primary vote of 25% in the poll suggested the result was “about 50/50 two-candidate preferred”.

“After five days of campaigning I’m really uplifted by that result, it shows a 13% swing against the Nationals already,” he said. “And it also shows a level of frustration within the community about local and national politics that is going to be expressed at the ballot box.”

Oakeshott said the campaign was “not about me, it’s about an area responding positively to the frustrations of flat-lining politics”.

He said issues of concern to voters included lack of progress on the national broadband network, climate change, tax reform and Indigenous recognition.

At the local level, Coffs Harbour being the last segment of the Pacific Highway bypass to be completed and Hartsuyker’s record on TAFE during his stint as vocational education minister were concerns.

Despite the encouraging result for Oakeshott, Hartsuyker could win with preferences from the Christian Democrats, who polled 3.6%, and a share of the 6.9% of undecided voters.

When asked to make a selection, more undecided voters backed the National (45.8%) than Labor and Oakeshott, who each got 11.9%.

The national director of GetUp, Paul Oosting, said the results “look good” for Oakeshott and put him “within striking distance of returning to parliament”.

“As a long-standing advocate of integrity in politics and as a candidate who will seek reform, Mr Oakeshott will be opposed by those who seek to maintain the status quo of shadowy donations that undermine confidence in the current system,” he said.

GetUp is campaigning in the election to strengthen democracy by reducing the power of corporate interests. It will hand out how-to-vote cards to help voters pick candidates that “want to clean up politics, get the money out and the good guys in”, Oosting said.

He said Oakeshott was “a passionate advocate for ending the practice of mining companies and property developers buying influence”.

Hartsuyker was contacted for comment.