With the very real prospect of Tony Windsor challenging Barnaby Joyce for the seat of New England, Joyce, in true Coalition style, has reached for the dirt file.

In an interview with ABC’s Radio National on Monday, Barnaby brought up Tony’s property dealings, implying that he had made a large personal profit from a policy he is now protesting against – coal mining on the Liverpool Plains.

Joyce pointed out there was an existing mine at Werris Creek that “was formerly owned by a person called Mr Windsor who made millions and millions of dollars out of the sale of it”.

“I think it’s just a little bit convenient when 30km away from one mine is another mine which Mr Windsor made himself a multi-millionaire out of,” he said. “Congratulations, that’s a commercial contract. The fact is that, basically it was a 99-year lease, Mr Windsor turned himself into a multi-millionaire, got the place back at a peppercorn lease rate and I think he got his neighbour’s place back at a peppercorn lease rate as well.”

Windsor has previously defended the sale of his family’s land to a Whitehaven subsidiary in 2010, explaining it was adjacent to a small existing mine and was not on the Liverpool Plains and did not have significant water resources underneath it.

“It was put in about 80 years ago,” he told 2GB in July. “They [the company] wanted to extend that mine … the farmer has no right over their land if in fact a natural resource is found. On a small portion of some country that we owned, it was found. They wanted to mine it. If, in fact, push came to shove, they would have mined it through the land and environment court. So there’s processes that override the landholder.”

Regarding the proposed Chinese owned Shenhua coal mine, Windsor said “I think it’s an atrocious decision, not because of agriculture but because of water. Here we have this magnificent piece of land, underlain with the biggest groundwater system in the Murray-Darling and they’re going to put that at risk because of the shonky arrangement that was put in place.”

In response to Joyce’s accusations on Monday, Windsor demanded an apology with a threat to sue if it was not forthcoming and a warning to get his facts straight.

People in glass houses shouldn’t throw stones. And Barnaby is in no position to throw stones.

In 2006 and 2008, the Joyce’s bought two neighbouring properties totalling 2400 acres in the Pilliga. The locals couldn’t understand why because the land was no good for farming.

A successful farmer and exporter from a nearby area said of the Joyce’s purchase ”This is scalded country. It could not support the number of animals that would be needed to make a return on investment,” he says. ”It is a strange buy, put it that way.”

Rumours abounded.

One was that the land would have to be bought back to build the inland railway, which is a long-term infrastructure policy of the National Party.

The other theory among locals was that Joyce must have bought with plans to cash in on mineral wealth in the area.

Denis Todd, a farmer from nearby Baradine and a Warrumbungle Shire councillor, recalls a conversation he had with Joyce at a petrol station in about 2009.

”I asked him, ‘Why did you buy that mongrel country out there? You could have bought better grazing land closer to St George,”’ Todd says.

According to Todd, he asked Joyce if he had bought to take advantage of the coal known to run throughout the Pilliga. Todd says Joyce responded: ”The coal’s too deep but there’s plenty of gas there.”

In 2005, the year before the Joyce’s first acquisition, Eastern Star revealed it had already spent $50 million exploring the Pilliga, mainly around Narrabri, since 2001.

At a time when few people had even heard the term ”coal seam gas”, the company had plans for 1100 gas wells dotted across the Pilliga, feeding a $150-million pipeline to the Hunter Valley.

Joyce’s property at Gwabegar lies inside the ”petroleum exploration licence” (PEL) areas that Eastern Star – before it was sold to Santos – owned the right to explore.

By 2007 – between the first two purchases made by the Joyces – CSG companies were boasting of gas reserves to the east, west and south of the properties.

All indications at this time were that the gas rush was coming.

In October 2007, Eastern Star Gas Limited announced that the former deputy prime minister (but then still-serving MP) John Anderson had been appointed chairman of the company.

A former Nationals leader, Anderson is a political ally and personal friend of Joyce and was his campaign manager in his bid to win the seat of New England in the 2013 election.

Despite this close association, Joyce maintains he had ”no knowledge at all” that the Pilliga would be at the eye of the CSG rush when he bought his land.

Joyce has proposed that a landowner get 1 per cent of the well head revenue of a CSG well. The best performing well in Queensland produces $1 million a day but an average CSG well is worth about $60,000 a day. At that rate, a single well would earn a landholder more than $200,000 a year before tax.

National Party elders, including Anderson, have been criticised for aligning too closely with mining interests over the traditional farming constituency. Mark Vaile, who succeeded Anderson as National Party leader, became a chairman of Nathan Tinkler’s ill-fated Aston Resources when he left Parliament. Former NSW leader Ian Armstrong worked as a lobbyist for AGL.

When Joyce’s land was brought up after his previous attempt to smear Windsor before the 2013 election campaign, he replied ”I’m happy to sell it, it’s for sale.” Adding: ”If someone wants to take it off my hands and make a million dollars, go right ahead.”

Later, Joyce revealed that he had instructed a local land agent to sell if he can get the right price. He said he understood the ownership could be ”viewed as a conflict of interest”.

According to his latest statement of pecuniary interest, Joyce still owns the property.