Low Mill on Gresley Road in Keighley dates back to 1779 and was powered by water diverted from the River Worth through a series of sluices and a goit.
But the building has been derelict for decades, and last year it was added to Save Britain’s Heritage’s At Risk register of buildings that face an uncertain future.
Bradford Council has revealed that it has begun an investigation after the historic water features on the site were recently concreted over.
Details of the investigation were discussed at a meeting of the council’s Bradford Planning Panel at a meeting on Wednesday.
Members were discussing a planning application to build a steel fabricating workshop in front of the site.
The application had been submitted by JCL Machinery Limited, who had bought a section of the site after the damage was done, unaware of the unauthorised work which had been done by a previous owner.
Part of the development site included in the plans is the former water feature area.
The application had said the workshop had been designed to “echo the style of the mill” and would not harm the setting of the existing building.
A heritage statement included in the application, written by Craft Design and Build, acknowledged the concerns about the unauthorised works, saying : “Had we have been consulted sooner we would have advised the client not to obtain the site.”
Although the plans had attracted 28 letters of support, with people claiming the work would create jobs and improve an eyesore site, heritage organisations raised serious concerns about the plans.
Historic England had said of the application: “The mill is highly significant for a number of reasons including the early date of construction, the fact that it was a cotton mill (unusual in this area) and the association with Sir Richard Arkwright, renowned industrial engineer.
“The application site is to the west of Low Mill and lies over the former waterways and sluices that fed the eighteenth century internal waterwheel of the mill. These constituted an important curtilage component of the listing but appear to have been destroyed relatively recently.
“The destruction of the water management system constitutes an act of heritage crime.”
The West Yorkshire Archaeological Advisory Service said the mill was “of national and arguably international significance in the development of the region’s textile industry.
“The mill is amongst the county’s first purpose built textile mills and reputedly the earliest to employ a steam engine to augment water power.”
A report to the committee had suggested that the application be refused due to the impact on the listed mill, and the fact that it could prejudige the future development of the site.
It added: “The investigation into the destruction of the former waterways and sluices that fed the internal waterwheel of the mill is an ongoing matter.”
Planning officer Andrew Moxon told the committee: “This site is subject to an enforcement investigation. The land has been altered and the historic water sluices and goits have been destroyed.
Chris Hinnit, representing the applicants, said: “It is very unfortunate about the history of this site. My client took the property on face value, not knowing about the previous infilling of the waterway by the previous owner.
“This proposal seeks to bring new life into the area, and has public support. it would be a shame to see this refused. We can’t change the past.”
Legal officer Bob Power said approving the application could cause issues should the council decide to take further action.
He said: “If the authority decided to served a Listed Building Enforcement for the features to be restored, the developer could have problems if their car park is over these features. That is quite a big issue I’d say.”
Coun Paul Godwin (Lab, Keighley West) said: “If we approve it and the development goes ahead we could be in a potential legal minefield. We can’t approve this until we have this issue sorted.”
Planning manager Mark Hutchinson confirmed an investigation had begun, but could not give too many details during a public meeting. He said the council had yet to issue an enforcement notice.
He said: “Anything that adds to this site will be compounding the harm that has already happened.”
Mr Power suggested members defer the decision, as the outcome of the investigation could have a big impact on their decision.
After hearing about the criminal investigation, members voted to defer a decision on the workshop application until the investigation had progressed.