A Freedom of Information request made by the campaigners at the Contentious Tax Group found there were more than 93,000 complaints made about the department in 2024-2025, external.
This was an increase from just over 70,000 in 2020-21, with one of the main gripes about poor response times.
Quantexa says automated decisions about tax payers made by AI will still need to be checked by people.
Quantexa chief executive Vishal Marria told the BBC the new technology was designed to “support human decision-making, not replace it”.
“In government environments, AI cannot operate as a black box. Decisions need to be transparent, auditable, and explainable, particularly in areas affecting citizens directly,” he said.
He also said HMRC data would remain secure, and staff working with the government department would remain separate from the rest of the business.
“We never take HMRC data away from the HMRC environment,” he added.