AI in capital letters with judicial gavel in front

The Hidden Risk of AI: Why You Must Still Check Tax Sources

7 May, 2026

Artificial intelligence is transforming how tax professionals access information, offering quick explanations and summaries of complex rules. However, recent confusion around UK VAT deadlines highlights a key risk: AI-generated answers can be confidently wrong. Without checking authoritative sources, this can lead to costly compliance errors.

AI tools produce clear, confident responses, which can create a false sense of reliability. When an answer “sounds right,” users may accept it without verification.

A common example is the incorrect assumption that VAT deadlines automatically move to the next working day if they fall on a weekend or bank holiday. 

In VAT, the rule is clear: deadlines are fixed in law, and they do not change when they fall on weekends or bank holidays. 

HMRC confirms that VAT returns can be submitted on weekends and bank holidays. If businesses cannot file on those days, they must submit before the deadline, typically on the previous working day. 

For payments, timing is equally strict. Cleared funds must reach HMRC by the due date or earlier.  

This issue is not limited to AI tools. When researching VAT deadlines, it is clear that several professional firms’ websites also contain incorrect or conflicting information.

Some incorrectly state that deadlines move to the next working day. This creates a self-perpetuating misconception, as: 

  • AI systems may learn from and repeat these errors
  • multiple sources appear to confirm the same incorrect rule
  • users gain false confidence from repeated misinformation

In reality, this demonstrates how easily errors can spread, even across professional content.

AI errors often arise because it recognises patterns, not legal authority, it treats conflicting sources as equally valid and it may generalise rules across different taxes. For example, many non UK countries do permit submission on the first day following a weekend or public holiday deadline, which is what may have led to the initial error.

The growing use of AI also raises professional and ethical considerations. Professional Conduct in Relation to Taxation (PCRT) and its AI topical guidance explicitly requires members to exercise professional judgement, due care, and appropriate verification of information.

Responsibility for advice remains with the professional, not the tool. Treat AI with the same, if not more, professional scepticism that you would a report produced by an eager to please tax junior.

In other words, using AI does not reduce professional responsibility, it increases the need for critical review.

AI remains useful, but only with proper safeguards:

  • check authoritative sources - use GOV.UK, HMRC manuals, and recognised professional bodies
  • use AI as a starting point - not a final answer
  • be cautious of repeated claims - consistency across sources does not guarantee accuracy
  • follow professional standards - apply PCRT principles and verify all technical decisions
  • most AI search engines provide links to their sources - click through as the detail on the webpage does not always match AI’s interpretation.

The confusion around VAT deadlines shows how easily incorrect information can spread across AI tools and professional websites alike.

AI can assist, but it cannot replace authoritative guidance or professional judgement.

In tax compliance, accuracy is critical. Verifying information against trusted primary sources and applying established professional standards such as PCRT is not optional, it is essential to avoiding costly mistakes.