Of 83 people surveyed, 86% opposed the proposals while just 14% agreed with them.
The chartered accountancy firm said the results would be a blow to Treasury minister David Gauke, who is currently facing concerns by civil liberties groups and MPs over the risks of sharing such sensitive information.
The proposals were first introduced by HMRC last week. It said it planned to make anonymous tax data available to third parties including companies, researchers and public bodies. But it added that it would only share this information to generate clear public benefits.
According to HMRC documentation, officials are currently examining "charging options".
Since then, the government body has issued another statement assuring a rigorous accreditation process for anyone wanting access to the tax data, with all inquiries being subjected to the same confidentiality provisions faced by HMRC staff. It said this included criminal sanctions for the unlawful disclosure of taxpayer information.
Baker Tilly’s senior tax partner George Bull said: “With no clear business case for making taxpayer data widely available, with no intention to make money from the data other than to cover the costs of providing it, and in the face of inevitable concerns regarding confidentiality, the initiative seems misguided.
“Leaving aside the government’s historically dismal track record of keeping confidential information confidential, there seems to be no recognition that the compilation of HMRC’s data with data acquired from other sources would lead to the identification of many individuals.
“HMRC may not have broken rules of confidentiality, but adding huge volumes of tax data to what is already available risks eroding the privacy of millions of powerless taxpayers.”
Tax partner at Edwin Coe, Frank Strachan, was also critical of the proposals: “When I first learned of this issue I had to check it wasn't April Fools Day,” he said.
“As a taxpayer myself I don't want my data being sold to anyone, so I hope that HMRC, and more importantly the politicians to whom HMRC are accountable, realise the strength of public opinion against this ridiculous idea and stop it dead in its tracks.
“HMRC are paid by taxpayers to collect the correct amount of tax from the population and it should not be in the business of selling data, however anonymised it may be, to anyone.”
