HMRC rolls Microsoft Copilot out to 28,000 staff after Whitehall trial

TL;DR:

• HMRC has licensed Microsoft Copilot for around 28,000 staff and is preparing agentic features for use up to “Official Sensitive” workflows.
• Chief AI officer James Mitton wants HMRC to be “the most AI-enabled tax authority on the planet”, citing a Cabinet Office trial that recorded 26 minutes saved per user per day.
• For UK taxpayers and businesses, the deployment puts a generative tool inside the country’s largest data-rich enforcement department, while the same Whitehall trial flagged limits on complex, sensitive work.

HMRC has begun one of the largest single Copilot rollouts in UK government, licensing Microsoft’s assistant for around 28,000 officials and preparing to switch on agentic-style features. Speaking at the Think AI for Government event in London, HMRC chief AI officer James Mitton framed the move as part of an ambition to make the department “the most AI-enabled tax authority on the planet” and offer staff “fairly potent AI tools that they can safely play with”.

The decision rests heavily on a 2025 Cabinet Office trial across roughly a dozen departments, including HMRC. Participants reported saving an average of 26 minutes a day, with more than 70% saying Copilot cut time spent searching for information and 82% saying they would not want to give it up. The same evaluation, however, flagged “limitations… when dealing with complex, nuanced, or data-heavy aspects of work” and concerns about handling sensitive data — caveats that sit awkwardly with HMRC’s plan to use the tool inside Official Sensitive processes.

Context for UK businesses and taxpayers

HMRC already credits earlier automation with around £8 billion in additional tax-gap recoveries, framing Copilot as a productivity overlay on existing systems rather than a redesign. That positions the rollout closer to recent enterprise patterns, including Accenture’s firm-wide Copilot deployment to 743,000 employees announced this week, than to bespoke government-only AI builds. It also lands in a Whitehall IT estate where stale and duplicated gov.uk content has previously fed AI systems with conflicting information — a risk amplified when 28,000 caseworkers can ask a model about live tax matters.

For UK taxpayers and SMEs, the practical implication is that interactions with HMRC over the next year will increasingly be drafted, summarised or triaged with Copilot in the loop. Once staff routinely lean on the tool for correspondence and case notes, withdrawal becomes politically and operationally difficult, even if specific outputs prove unreliable. Stakeholders likely to feel this first include accountants and payroll providers responding to letters, agents handling enquiries, and businesses contesting assessments.

Looking forward

The next test is whether HMRC publishes hard accuracy and complaints data alongside the productivity claims. The Whitehall trial’s own warnings about complex work mean a 26-minutes-a-day average is a weak proxy for whether decisions on Official Sensitive cases are better, worse or merely faster. UK businesses dealing with HMRC should plan for a near-term environment in which Copilot is embedded by default, and lobby through professional bodies for transparency on where in the process the model is — and is not — relied on.