If you’ve filed a tax return that doesn’t quite match what your bank statements, property records, or online selling activity say about you, there’s a decent chance HMRC already knows before you do. The tool behind that is called Connect, and it’s been quietly reshaping how HMRC picks who to investigate for well over a decade.
This guide covers what Connect actually is, what data it pulls from, how it flags people, and what you should do if you think you might be on its radar.
- What is HMRC Connect?
- How does HMRC Connect work?
- What data does it use?
- What can trigger an HMRC enquiry?
- What happens if Connect flags you?
- Can Connect get it wrong?
- How to reduce your risk
- Frequently asked questions
What is HMRC Connect?
Connect is HMRC’s data-matching and risk-analysis system. It was introduced in 2010 and has been expanded steadily since, with HMRC investing tens of millions of pounds in it over the years. Its job is straightforward: pull together information from dozens of different sources, cross-reference it against what taxpayers have actually declared, and flag the gaps.
HMRC has been careful to say Connect itself isn’t an “AI system” in the generative sense, it’s closer to a very large, very thorough data-matching engine. That said, HMRC has also been investing separately in AI tools to support its compliance staff, so the direction of travel is toward more automated risk-scoring, not less.
The scale is the point. Connect is reported to hold in the region of 55 billion individual data items, and it was central to HMRC recovering an estimated £4.6 billion in additional tax during the 2024/25 tax year alone. That’s not a small side project. It’s now one of the primary ways HMRC decides who gets a letter.
How does HMRC Connect work?
Connect doesn’t read individual tax returns and decide something looks off in isolation. It works by cross-referencing, building a picture of your income, assets, and spending from multiple independent sources, then comparing that picture to what you’ve declared.
If your declared income doesn’t line up with your lifestyle, your property, your bank interest, or your online sales activity, Connect flags the mismatch for a human caseworker to review. It doesn’t automatically open an enquiry. It surfaces the case, and HMRC decides from there whether to act.
What data does it use?
Connect draws on a wide range of sources, including:
- Self assessment and corporation tax returns already filed with HMRC
- Land Registry records, covering property purchases, sales, and value
- DVLA vehicle registration data
- Bank and building society interest reports
- Common Reporting Standard data shared by tax authorities in over 100 countries, covering offshore bank accounts and investments
- Companies House and DWP records
- Online marketplace and platform data, including sales through eBay, Airbnb, and similar platforms
- Land and property rental listings
The common thread is that most of this data doesn’t come from you. It comes from third parties who are legally required to share it with HMRC, which is exactly why trying to simply leave something off a return rarely works as a strategy.
What can trigger an HMRC enquiry?
Some of the most common mismatches Connect picks up on:
- Bank interest reported to HMRC by your bank that’s higher than what you declared
- A property sale or purchase that doesn’t match your declared income level
- Rental income from a platform like Airbnb that hasn’t been declared on a self assessment return
- Regular selling activity on eBay or similar platforms that looks more like a trading business than occasional decluttering
- Offshore account interest or gains reported under the Common Reporting Standard with no matching UK disclosure
- A VAT-registered business whose declared turnover doesn’t match its card payment or online sales volume
None of these on their own guarantee an enquiry. Connect is a filter, not a verdict. But each one raises the odds that a caseworker takes a closer look.
What happens if Connect flags you?
Being flagged by Connect doesn’t automatically mean an investigation. In practice, HMRC’s response usually follows one of a few paths.
A nudge letter, asking you to review a specific area of your return and correct it voluntarily if needed, often with no formal enquiry opened at all. A formal compliance check, where HMRC writes to you (or your accountant) requesting specific information or documents. A full enquiry, opened under Section 9A of the Taxes Management Act 1970 for individuals, or the equivalent corporation tax enquiry powers for companies, which can go significantly further and cover multiple tax years if HMRC suspects a pattern.
If you receive any of these, the worst response is to ignore it or hope it resolves itself. HMRC enquiry windows and penalty exposure both get worse the longer something goes unaddressed.
Can Connect get it wrong?
Yes, and this is worth taking seriously rather than dismissing. Connect matches data points, it doesn’t understand context. A property sold to fund a divorce settlement, an inheritance that looks like undeclared income, a joint account where the interest belongs mostly to your spouse, all of these can trigger a flag that has a perfectly ordinary explanation.
This is exactly why, if you do receive a letter referencing a discrepancy, the right response is a clear, evidenced explanation, not silence and not panic. A false positive is usually resolved quickly once the full picture is on the table. What draws things out is when nobody responds properly to the initial query.
How to reduce your risk
The most reliable way to stay off Connect’s radar isn’t to guess what it’s looking for. It’s simpler than that: declare everything, on time, and keep records that back up what you’ve declared.
That means declaring all rental income, including short lets and Airbnb income, in the correct tax year. Reporting bank interest accurately, since your bank is already telling HMRC the figure. Treating regular online selling as a trading activity if that’s genuinely what it is, and registering as self-employed where the rules require it. Disclosing offshore income and gains where they exist rather than assuming they won’t surface. Keeping business records that would hold up if HMRC asked for them tomorrow, not in six months.
If you’ve realised something in a previous return wasn’t quite right, HMRC’s disclosure facilities exist for exactly this. Coming forward voluntarily, before Connect flags it, generally leads to a far better outcome on penalties than waiting to be caught.
How we can help
If you’ve had a letter from HMRC referencing a discrepancy, or you’re simply not confident your returns would hold up under this level of scrutiny, it’s worth getting a second set of eyes on it before you respond. We handle self assessment, corporation tax, VAT returns, and annual accounts for clients across a range of industries, and we deal directly with HMRC on your behalf where an enquiry is already underway. Getting this right the first time is always cheaper than correcting it after the fact.
Frequently asked questions
Is HMRC Connect actually artificial intelligence?
Not in the way the term is usually used. HMRC describes Connect as a data-matching and risk-analysis tool rather than a generative AI system. It cross-references information rather than making independent judgements, though HMRC is investing in AI more broadly to support its compliance teams.
Can HMRC see my bank account through Connect?
Connect receives interest figures reported by UK banks and building societies, and under the Common Reporting Standard, similar data from banks in over 100 other countries. It doesn’t give HMRC a live view of your transactions, but it does receive regular summary reporting.
Does selling on eBay or Vinted trigger an HMRC investigation?
Occasional selling of your own possessions isn’t taxable and shouldn’t trigger anything. Regular, repeated selling that looks like a trading activity is a different matter, and platforms are required to report seller data to HMRC. If you’re unsure whether your activity counts as trading, it’s worth checking rather than assuming.
What should I do if I get a letter from HMRC about a discrepancy?
Don’t ignore it, and don’t respond without understanding exactly what HMRC is asking. Gather the relevant records, and if anything is unclear, get advice before you reply. Response deadlines matter, and an incomplete or rushed answer can make things worse.
Will HMRC tell me if Connect has flagged my return?
No. Connect works in the background, and HMRC doesn’t notify you that you’ve been flagged, only if and when they decide to act on it, usually through a letter or compliance check.
