Wellingborough Council is urging residents to be extra vigilant when dealing with contractors that knock at their door offering home insulation.
The warning comes after a number of people reported being visited by a company claiming to be part of the local authority's scheme offering free cavity wall and loft insulation.
The council's scheme is only offered through supplier Snug Network and installer Energy Care Group and will never use cold calling or door to door sales teams. The professionally-installed insulation aims to help residents reduce their energy bills, which are now more than £1,300 a year for the average household.
Councillor Peter Morrall, chairman of the council's community committee said: "These contractors are calling on people without any warning claiming to be working on behalf of the council and this is worrying. We do offer a scheme for free insulation but our contractors will never phone or turn up unannounced. We're not saying that all cold-callers are bogus, but we don't want people to commit to something that they mistakenly believe to be directly associated with Wellingborough Council.
"With any doorstep callers, we would advise people to check ID, and look for company logos, headed paper, business cards and uniforms to satisfy themselves that the contractor is genuine. Any legitimate contractor will be more than happy to arrange to call back later, giving people time to do a quick background check by phoning the company or the council.
"We know that we've had a number of scams operating recently in the borough so we'd ask people to take extra care, not only with doorstep callers but also with too-good-to-be-true deals that appear through the post, over email or by phone. If anyone suspects a scam we'd ask that they let us know, as it's only by sharing the information and warning people that the issue can be stopped."
For more information about the free cavity wall and loft insulation provided by the council, or to report a suspected scam, residents can call 01933 229 777.