A New South Wales Liberal branch president has declared war on the National party in the heart of Michael McCormack’s own seat, organising with Anyone But Nats to help defeat the Coalition partner at the NSW election.

Wagga Liberal branch president Colin Taggart has unleashed on the Nationals ahead of the state and federal elections, which the Coalition will struggle to win.

“The Nats are plagued by scandal, vested with bullies and riddled with incompetence,” Taggart told Guardian Australia. “The one thing they were supposed to be good at were looking after farmers and they have failed at that. Look at the management of the Murray-Darling.

“They are a barnacle on the backside of a major party, they get less votes than the Greens, yet they exercise more power over us.”

The development presents another headache for McCormack in a difficult year for the Nationals. In the past 12 months, Barnaby Joyce was forced to step down as leader over sexual harassment allegations after his affair with a staffer and Andrew Broad will not recontest the next election following the “sugar baby” revelations.

The party is also facing serious questions over its management of the Murray-Darling at a federal and state level following a massive fish kill last week – an event the Nationals put down to low water levels due to drought.

Taggart has invited Liberal members in the Wagga electorate to a meeting on Saturday to discuss the deal to allow a National candidate, Mackenna Powell, to run at the seat in the state election without a Liberal challenger. Normally, there would be a three-cornered contest in a non-Coalition seat.

He said his branch largely blames the National party for undermining Liberal candidate Julia Ham in the 2017 state byelection, which saw the Liberals lose the seat to rural independent Joe McGirr.

Taggart said he warned his friend and local federal MP, McCormack, at the time of the byelection in an email that it would cause trouble in the Coalition relationship.

“The Nats were criticising the way she was dressing,” he said. “It was mean, spiteful and sexist.”

After the byelection result, a bitter fight broke out, with Nationals upper house MLC Wes Fang confirming to the Australian he had sent abusive text messages to fellow Liberal MLC Matthew Mason-Cox, after Mason-Cox was critical of the National party’s role in the loss.

The tension has now boiled over again, with members of the Wagga branch set to discuss the motion: “If the Liberal party will not run an endorsed candidate in March, this [State Electoral Conference] resolves to support an independent Liberal.”

In a members’ email, Taggart wrote: “Wagga has never been represented by the Nats and never will be with your help and support.”

Taggart has vowed he will stand as an independent Liberal if no one else will represent Liberal party values – describing the Nationals as “agrarian socialists”.

“I think Joe will win, I know him well, he is a champagne socialist but a lovely bloke,” Taggart said. “But I think we should be running an independent candidate to show Liberal voters we have an alternative to the Nats.”

The Nats are plagued by scandal, vested with bullies and riddled with incompetence. Wagga Liberal branch president Colin Taggart

He contacted Rohan Boehm, a co-founder of Anyone But Nats, even though the movement has campaigned strongly on issues such as climate change and coal seam gas, which Taggart described as “lefty” issues.

Taggart has also invited Cory Bernardi’s Australian Conservatives, David Leyonhjelm and One Nation’s Mark Latham into the seat ahead of the election.

“My essential point is my enemy’s enemy is my friend,” he said. “I am in a bind because I want to vote for Coalition but I don’t want a triple lock here – a Nat in the upper house in [upper house MLC] Wes Fang, Michael McCormack federally and then a Nat at state level.

“People need to know they have other choices.”

Taggart is a Belfast immigrant who publishes corporate magazines and moved to Wagga 15 years ago with his Wagga-born wife. He has been active in the party for 15 years, a member for six years and president for two years.

Last year’s Wagga byelection was brought on by the resignation of former Liberal MP Daryl Maguire, after being caught discussing potential developer “dividends” over a multimillion-dollar property deal with Chinese developers and Canterbury city council.

Taggart accused the Nationals of betraying the Coalition in order to take Wagga from the Liberal party, which had held it for 60 years. The deal meant if the Liberals lost the byelection, the Nationals would get to run at the state election – an outcome which Taggart says “perversely incentivised” the Nationals to disrupt the byelection.

In his notice to Liberal members, Taggart wrote: “The National party cannot represent Liberals and the people of Wagga.

“By initially threatening to cross the floor, the Nats caused an early byelection for which we were ill prepared – that was an act of bastardy: not what one would expect from friends and Coalition partners.

“They undermined the Liberal campaign and in large part contributed to the defeat of our candidate. They also deprived Liberals of the opportunity to put forward a candidate in March.

“Liberals cannot and will not reward that treachery by electing a Nat to the seat of Wagga. If the Nats are elected, Liberals will never be able to field a candidate again and the party is effectively dead in Wagga.”

He took action as president because of the “white hot rage amongst the Liberal matriarchs”, who had worked so hard raising money through cake stalls and card games.

Taggart said that ideally the branch would like to see a Liberal candidate stand in a three-cornered contest in March and at every election but he admitted it was a little late to organise now as a result of the Coalition deal.

But he said it was “galling” to see the NSW Nationals leader, John Barilaro, McCormack and the National candidate all at the opening of stage three of the newly revamped Wagga Hospital when McGirr, the local independent member and doctor, was not even invited.

He said the stoush would not be contained to the state election and also accused sections of his own party of arrogance. He said he believed the Coalition agreement between the Liberals and the Nationals needed to be made public and voted on by the Liberal state council for approval.

Taggart said the failure of the Liberal party to fully implement reforms that would see every member get a vote on preselections reflected the “arrogance of party elites”.

“The Liberals haven’t respond well to calls for democratisation,” he said. “They rolled [senator] Jim Molan, a fine Australian, because we didn’t get democratic reforms through. The party seems beset by this moderate faction, so they just say ‘leave it up to the Nats’.”

McCormack and Fang’s offices both said Taggart’s motion was an internal matter for the Liberal party. Guardian Australia has also sought comment from the NSW National party office. A spokesman for NSW Liberal party said the party had already announced its intention not to contest the Wagga byelection.