The Local Government and Social Care Ombudsman (LGSO) investigated the authority after the resident complained about its handling of an application by the business in question for a certificate of lawfulness of use.
According to the ombudsman’s report, published earlier this month, a resident known as "Mrs X" complained in 2016 that a local business was encroaching onto nearby land with vehicles and machinery despite the land being subject to a restrictive covenant forbidding such uses.
On investigation, the council found that the business owner was using the land in an unauthorised way, in breach of planning controls, and ordered him to remove the equipment.
In response, the business owner, known as "Mr Y", applied under Section 291 of the Town and Country Planning Act 1990 for a certificate to confirm the lawfulness of his use of the land.
As part of the application, Mr Y made a declaration saying he used the land for storing vehicles, plant and machinery before he bought it in 2004 and had continued doing so since.
That application, the ombudsman found, was subsequently published online to allow residents to view and comment on it.
Mrs X responded by publishing evidence that countered Mr Y's claim that the land did not have any vehicles stored on it until 2014.
This in turn prompted a response from Mr Y in a second statutory declaration, but the council did not make this public.
The report states: "Mrs X says had she been aware of what he had said she could have rebutted it."
It goes on to say that Mrs X "says the council failed to follow due process and decided the application without all relevant information".
"But for that fault Mrs X believes the council would have refused the application and prevented the continued use of land near her home."
In his analysis of the case, the ombudsman wrote: "The council’s policy is to publicise applications for a certificate.
"Where it has such a policy the ombudsman expects it to follow that policy.
"The council failed to upload the second statutory declaration contrary to its publicity policy. I find it acted with fault in doing so.
"Publishing the second statutory declaration on the website would have enabled Mrs X to present further evidence to rebut what Mr Y had said.
"This failure denied her that opportunity."
However, while finding that the council was "at fault in failing to follow its policy and practice", the ombudsman found that this failing "did not affect the final decision".
Planning approached Wiltshire Council for a comment, but it had not responded by the time of publication.
Last week, Planning reported that Leeds City Council had been reprimanded by the LGSO for failing in its consideration of a planning application for householder development to "properly assess" the potential impact of the works on a neighbouring property and had been asked to make a payment to the complainant.
Planning also recently reported that the LGSO had found fault with nearby Wakefield Council for failing to properly assess amended plans for a garage redevelopment and for taking too long to respond to a neighbour's complaint about it.