On 23 June 2026, HMRC put a number on how much tax goes unpaid every year, and that number is £59.2 billion.
That figure is the UK tax gap, and buried inside it is a message every private landlord should read carefully. Small businesses, the group HMRC uses to classify most individual and unincorporated landlords, account for 62% of the entire gap. And the single biggest reason for it is carelessness.
If you let a property in your own name, this article explains what the latest tax gap figures mean for you, why HMRC has both the resources and the data to come looking, what an enquiry actually costs, and the one move that separates a manageable outcome from an expensive one.
Key Takeaways
- HMRC's Measuring Tax Gaps 2026 report, published on 23 June 2026, estimates that the UK tax gap for 2024/25 stands at £59.2 billion
- Small businesses, the group that includes most individual landlords who let property in their own name, account for 62% of the UK tax gap, up from 40% in 2017/18
- Failure to take reasonable care is the largest single behavioural cause of the tax gap, accounting for 35%, or approximately £20.8 billion, highlighting that carelessness contribute more than deliberate tax evasion
- HMRC has been allocated £1.7 billion to recruit 5,500 additional compliance officers and achieved a record £48 billion in compliance yield during the 2024/25 tax year
- HMRC can normally open enquiries into tax returns going back four years, extend this to six years where errors are deemed careless, and up to 20 years where tax has been deliberately understated, under sections 34–36 of the Taxes Management Act 1970
- Making a voluntary disclosure through HMRC's Let Property Campaign can significantly reduce the penalties payable, with some landlords seeing penalties reduced from substantial percentages of the tax due to little or, in certain circumstances, no penalty at all
What Does the £59bn UK Tax Gap Mean?
The £59.2 billion UK tax gap is the difference between the amount of tax HMRC expected to collect and what it actually received during the 2024/25 tax year. While that may sound alarming, HMRC still collected £865.2 billion, or 93.6% of all tax due. In percentage terms, the tax gap has fallen from 7.5% in 2005/06 to 6.4% today, showing that overall compliance has improved over the long term.
For landlords, however, the headline number is less important than where the unpaid tax comes from. HMRC groups taxpayers into different customer categories, and the small business group — which includes most private landlords who let property in their own name — accounts for 62% of the total tax gap, up from 40% in 2017/18.
This does not necessarily mean landlords are becoming less compliant. HMRC says part of the increase reflects improvements in how it measures the tax gap. What it does mean is that the department now has a much clearer picture of where tax is being lost and which groups present the greatest compliance risk. For landlords, the takeaway is that property income is receiving closer scrutiny than ever before.
Are Landlords Now In HMRC's Firing Line?
Yes. While HMRC has not publicly singled out landlords as a specific enforcement target, several recent developments mean they are more likely to face scrutiny than in previous years.
First, HMRC now has significantly greater capacity to investigate underpaid tax. The Spending Review 2025 allocated £1.7 billion over four years to recruit 5,500 additional compliance officers and 2,400 debt-management staff. That investment is already delivering results, with HMRC reporting a record £48 billion in compliance yield during 2024/25. Put simply, compliance activity generates substantial additional tax revenue, giving HMRC every reason to continue expanding it.
Second, HMRC has more information about landlords than ever before. Its Connect system cross-checks data from sources including Land Registry records, tenancy deposit schemes and, since the DAC7 reporting rules took effect on 1 January 2024, income reported directly by platforms such as Airbnb and Booking.com. If you receive rental income, there is a good chance HMRC holds information that can be used to verify what you report on your tax return.
Finally, the latest tax gap figures show where HMRC believes much of the missing tax arises. Most private landlords who let property in their own name fall within the small business customer group, which accounts for 62% of the UK's tax gap. More importantly, HMRC estimates that 35% of the tax gap results from failure to take reasonable care, compared with 12% from deliberate evasion. That suggests HMRC is looking not only for fraud, but also for ordinary taxpayers who have misunderstood the rules or made avoidable mistakes.
What Happens If HMRC Opens An Enquiry?
If HMRC opens an enquiry into your tax return, it will check whether you have reported your rental income correctly and paid the right amount of tax. If it finds that you have underpaid tax, it can demand the unpaid amount, charge interest and, in some cases, impose penalties. How far back HMRC can go depends on why the underpayment occurred.
HMRC normally has 12 months from the date you file your tax return to open a routine enquiry under the Taxes Management Act (TMA) 1970. However, it can still issue a discovery assessment even after that period if it later discovers that you underpaid tax.
The time limits are:
How Far HMRC Can Look Back | Applies When | Legislative Basis |
|---|---|---|
4 years | You took reasonable care | TMA 1970, s.34 |
6 years | You made a careless error that led to an underpayment of tax | TMA 1970, s.36(1) |
20 years | You deliberately understated your tax or failed to notify HMRC that you were liable to tax | TMA 1970, s.36(1A) |
The distinction between a careless and a deliberate error is critical. In Tooth v HMRC, the Supreme Court confirmed that HMRC must show conscious, intentional wrongdoing before treating an inaccuracy as deliberate. Carelessness on its own is not enough.
If HMRC concludes that you have underpaid tax, it may also charge a penalty under Finance Act 2007, Schedule 24. The amount depends on your behaviour.
Behaviour | Standard Penalty Range | Can HMRC Suspend the Penalty |
|---|---|---|
Careless | 0% to 30% | Yes (for up to 2 years) |
Deliberate, not concealed | 20% to 70% | No |
Deliberate and concealed | 30% to 100% | No |
Certain offshore inaccuracies (enhanced penalty regimes) | Up to 200% | No |
Within each range, HMRC considers the circumstances of your case. An unprompted disclosure, full cooperation and a genuine effort to help HMRC establish the facts can all reduce the penalty. Waiting until HMRC contacts you first usually results in a higher penalty than coming forward voluntarily.
Worked Example: How A Forgotten Flat Became An £18,000 Problem
Elizabeth bought a flat in Leeds several years ago. When she later moved in with her partner, she decided to keep the property and rent it out. She intended to declare the rental income each year, but after changing letting agents and losing track of the paperwork, she failed to include the rental profits on her tax returns for four consecutive tax years.
HMRC later identified the property and contacted Elizabeth to review her tax affairs. She had not deliberately hidden the income, but she still had to pay the tax she owed, together with interest and a penalty.
Assuming Elizabeth had under-declared £8,000 of taxable rental profit each year and paid tax at 40%, her position could look something like this:
Item | Amount |
|---|---|
Under-declared rental profit (£8,000 × 4 years) | £32,000 |
Additional Income Tax (40%) | £12,800 |
Carelessness Penalty (30%) | £3,840 |
Interest (Illustrative) | ~£1,500 |
Total | ~£18,140 |
Elizabeth was not a tax evader. She made a careless mistake (the largest behavioural cause of the UK's tax gap, according to HMRC). Had she corrected the error before HMRC contacted her, for example through the Let Property Campaign, she could have significantly reduced the penalty. If HMRC makes the first move, those reductions become much harder to achieve.
What To Do Before HMRC Contacts You
If you think you have underpaid tax on your rental income, don't wait for HMRC to contact you. Reviewing your tax affairs and making a voluntary disclosure as soon as possible can significantly reduce the penalties you face and demonstrate that you are taking steps to put things right.
For individual landlords, the Let Property Campaign provides a way to disclose previously undeclared rental income. After notifying HMRC, you will receive a disclosure reference and normally have 90 days to calculate and pay the tax, interest and any penalties due. The campaign is available to landlords with UK or overseas residential property, including those who live abroad but receive rental income from property in the UK. In many cases, coming forward voluntarily results in lower penalties than waiting for HMRC to identify the issue first.
Making a voluntary disclosure isn't just about reducing today's penalties. It also puts you in a much stronger position for the future. If your combined gross property and self-employment income exceeds £50,000, you are already within Making Tax Digital for Income Tax and must keep digital records and submit quarterly updates. This threshold will fall to £30,000 in April 2027 and £20,000 in April 2028, bringing many more landlords into the regime. Correcting any historic issues now and maintaining accurate digital records will make ongoing compliance much easier.
Conclusion
The tax gap statistics aren't an abstract Treasury headline. They are HMRC telling you, in its own numbers, which group it is resourcing up to pursue, and private landlords sit squarely inside it. The uncomfortable part is that the biggest driver isn't dishonesty; it's the honest mistake, made by someone who assumed their return was fine. That is precisely the position HMRC's 5,500 new officers are funded to find.
Whether a past error is careless or deliberate, whether a disclosure counts as prompted or unprompted, and which route protects you best are fact-specific judgements where getting it wrong is measured in thousands. If an HMRC letter has already landed. or you suspect one might, the time to act is before the next step is taken for you.
Worried About Your Own Undeclared Rental Income?
UK Property Accountants handles HMRC enquiries, voluntary disclosures and penalty negotiations for landlords across the UK and overseas.
FAQs
It is £59.2 billion, or 6.4% of all tax due, per HMRC's Measuring Tax Gaps 2026 report published on 23 June 2026.
Small businesses account for 62% of the gap. This is the largest share. This administrative group includes most individual and unincorporated landlords, which is why the figures matter directly to property owners.
Four years as standard, six years for a careless error, and twenty years for a deliberate error or a failure to notify chargeability.
If you have undeclared rental income, you should tell HMRC as soon as possible. Making an unprompted disclosure will generally reduce the penalties you face. The Let Property Campaign allows individual landlords to disclose previously undeclared rental income voluntarily.
If your combined gross property and self-employment income exceeds £50,000, yes — you came into scope on 6 April 2026. The income threshold drops to £30,000 in April 2027 and £20,000 in April 2028.
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