Australia’s biggest mortgage provider has declared a Queensland property with coal seam gas wells “unacceptable” as security for residential lending, raising fresh concerns that people living in the state’s gasfields may be unable to sell their homes.

But Queensland Gas Company (QGC), which owns the wells on the Chinchilla acreage, has insisted that no properties that host its infrastructure have had their values negatively affected.

A letter from the Commonwealth Bank, obtained by Guardian Australia, shows the presence of four wells on the 240-hectare property, currently on the market, was the sole reason given for refusing the owners’ application for a $500,000 bridging loan to buy a new home.

The application “fails to meet the bank’s lending criteria” because the Chinchilla property was “unacceptable” as security, despite being wholly owned by a couple with no outstanding debts or credit blemishes and a primary income reaching well past the top tax bracket.

“Long form valuation has revealed coal seam gas wells on the land, making the security unacceptable for residential lending purposes,” the bank said.

The owners then asked QGC if it would buy the property, but the company refused.

“QGC also does not agree with the assertion that its infrastructure has had a negative impact on the value of your property, or indeed any property currently hosting QGC infrastructure,” a letter from its landholder relationships manager said.

“QGC has found no direct negative impacts to the value of rural properties upon which resource activities are conducted within the Surat Basin.”

The manager’s letter said that “in QGC’s experience, an application for finance may be declined for a variety of reasons other than the value of the property proposed to be used as security”.

In a statement the Commonwealth told Guardian Australia it considered “a number of factors, including individual risk profiles and loan serviceability” when assessing applications.

“In some cases, we require an independent valuation to assist with our assessment of the loan application and to make sure we are meeting our responsible lending criteria,” it said.

Mark McGovern, a rural economics specialist from the Queensland University of Technology’s school of business, economics and finance, said the case could signal a wider unforeseen economic cost of the gas industry.

If the bank regarded property with gas wells as unsuitable security for a bridging loan, it followed it would not lend to people to buy such a property, McGovern said.

“Someone buying in as a resident wouldn’t meet the criteria of the Commonwealth bank,” he said.

The property owner, who asked to remain anonymous, said he and his wife had become “sort of prisoners in our own home”.

“We can’t sell it, we can’t lend against it. It’s useless to us,” he said.

His wife said she was “ropeable” on learning of the loan rejection after QGC had given public assurances its activities would not affect property values.

QGC offered to pay for an independent valuation of the property, but the couple already had two, as well as one from the bank before it overturned its pre-approval of the loan.

The Chinchilla man said their predicament was the latest sign that residents of Queensland’s gasfields, where property owners have no legal right to refuse gas companies access, were “the guinea pigs” for an industry since banned in Victoria and strongly resisted in NSW.

“We didn’t have the people power,” he said.

Anti-gas industry activists, a local property agency manager and the president of the Real Estate Institute of Queensland (REIQ) all told Guardian Australia it was the first case they had heard of a bank refusing to lend because of gas wells on a property.

Guardian Australia asked the Commonwealth Bank, Westpac, ANZ and National Australia Bank if gas wells now represented a black mark under their lending criteria.

A spokeswoman for Westpac said the bank dealt with properties “over a certain size” within its business/agricultural division, where “different lending principles [to residential loans] would apply”.

The Commonwealth Bank said in a statement that every loan application was assessed on a case-by-case basis and it did “not have a policy of excluding coal seam gas wells as acceptable security in our regional and agribusiness banking.”

ANZ and NAB did not respond.

The REIQ president, Antonia Mercorella, said it was concerning if the case represented “the start of a new trend where lending institutions were suddenly deciding they were not prepared to loan money to people wanting to buy these properties”.

“We know that in regional Queensland there’s a number of properties that this is going to create issues for,” she said.

“If they’re applying a blanket rule where they’re not going to give a loan to anyone who has these on their property, then that’s obviously concerning, because it would make it very difficult for those property owners to sell their property.

“There’s not too many buyers out there who are cashed up and able to buy without obtaining finance of the purchase.”

Lock The Gate organiser Phil Laird said it was the first known case of “something we have been concerned about for a long time … flat out whether a bank will lend money based on your security”.

“It feeds into a story of people who are in the gasfields and who are trapped,” he said.

“It’s going to make it very difficult for that guy to find another bank and what’s more, it’s going to make it difficult for a lot of people in similar circumstances to find someone and it’s going to cast a pall over their situation.

“There’s a lot of reasons why people need to move and change their property holdings and when some other party who’s been imposed on top of you starts to dictate the way in which you can conduct your life, your lifestyle, your succession planning, it becomes a real problem.

“And no one’s recognising this.”

Laird said the support underpinning the Queensland gas industry represented “a government-sponsored model to transfer risk on to the landholder”.

“There’s something fundamentally wrong about this. If you did this to BHP, Lend Lease or other large property holders, there would be hell to pay.”