HMRC is not standing still on undeclared rental income. The Spring Budget committed an extra £100 million to fund 500 new compliance officers, alongside £79 million earmarked for third-party debt collection over the next five years — on top of the 1,800 debt management roles already announced in the previous Autumn Budget. In plain terms: HMRC’s ability to find undeclared rental income is growing fast, and landlords who wait are taking on more risk with every month that passes.
The good news is that landlords who come forward under the Let Property Campaign before HMRC contacts them can pay meaningfully lower penalties and sidestep a full-blown investigation. This article breaks down exactly how much that difference is worth in practice, using real calculation examples, and what to do if you can’t pay everything you owe at once.
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Why Timing Changes the Penalty You Pay
The single biggest lever landlords have over their own penalty bill is when they come forward. Disclose voluntarily, ahead of any HMRC enquiry, and the penalty bands sit meaningfully lower than if HMRC opens a compliance check first. Once HMRC initiates that enquiry, the more favourable rates disappear.
This applies whether your rental income was never reported to HMRC at all, or whether you filed a return but left the property income off it — HMRC treats these as two separate situations, each with its own behaviour categories.
How HMRC Classifies Your Behaviour
Where a landlord never registered for tax and never filed a return covering the rental income, HMRC groups the reason into one of three bands:
- Non-deliberate — the omission stemmed from a genuine misunderstanding or circumstance, not an intent to avoid tax.
- Deliberate (not concealed) — the landlord knew the income should have been reported and chose not to, but took no further steps to hide it.
- Deliberate and concealed — the landlord not only withheld the income but actively worked to disguise it.
Where a return was filed but the rental income was left out or understated, a slightly different set of categories applies:
- Reasonable care — HMRC doesn’t set a fixed test here; it’s judged case by case, but landlords are generally expected to seek advice when they’re unsure of the rules and to file accurate figures.
- Careless — the return was wrong because reasonable steps weren’t taken to get it right, such as poor recordkeeping or overlooking a known obligation.
- Deliberate — the landlord knew the figures were wrong and submitted the return anyway, for example by understating rental income or overstating costs.
- Deliberate and concealed — the landlord not only filed an inaccurate return but took active steps to cover it up, such as producing a fabricated invoice for repair work that never happened.
What Actually Reduces Your Penalty
Beyond the behaviour category, HMRC also looks at the quality of the disclosure itself when setting the final penalty. A strong disclosure is scored across three elements:
- Telling HMRC about the problem — worth up to 30% of the reduction
- Helping HMRC understand what happened — worth up to 40%
- Giving HMRC access to the records behind it — worth up to 30%
The more complete and cooperative the disclosure, the more the penalty can be reduced from the maximum. For landlords weighing up their overall position, our tax-saving strategies guide covers the legitimate ways to manage the ongoing liability once everything is up to date.
Case Study: Failure to Notify (Ben’s Eight Properties)
Ben has owned eight rental properties generating income since the 2016/17 tax year, and never filed a tax return covering any of it. His annual rental income sat around £45,000, with net profits — after deductions and mortgage interest — starting near £33,000 and rising year on year. His PAYE employment income began at £80,000 and grew by roughly 3% annually.
Once the calculation runs through to 2022/23, Ben’s total unpaid tax comes to £113,969. Assuming his behaviour is classed as non-deliberate and he cooperates fully, working through the applicable penalty rates:
- Voluntary disclosure (before HMRC contacts him): total cost of £155,710
- Prompted disclosure (after HMRC contacts him): total cost of £167,107
That’s a difference of £11,397 — purely down to coming forward first.
There’s a further wrinkle: HMRC generally won’t accept the most recent tax year as part of a Let Property Campaign disclosure. So a landlord disclosing for 2023/24, for example, would typically be asked to file that year’s return separately, which then carries its own late filing and late payment penalties.
If that 2023/24 return were filed six months late, the numbers would look like this:
Late filing penalties:
- Initial penalty: £100
- Daily penalties (up to 90 days): £900
- Six-month penalty (the greater of £300 or 5% of unpaid tax): £999.30
Total late filing penalties: £1,990.30
Late payment:
- 5% surcharge on unpaid tax: £999.30
- Interest on the late payment: £771
Total estimated penalties for 2023/24 alone: £4,759.90
Landlords in Ben’s position want to know their exact exposure before they disclose, not after — this is exactly the kind of number our specialists work through on a discovery call.
Case Study: Inaccurate Returns (Ms Kim’s Rental Income)
Ms Kim runs a consultancy business that returned trading profits of £130,000 in 2018/19, growing at around 5% a year since. Alongside that, she owns two rental properties, cash-purchased with no mortgage, which brought in £28,000 gross in 2018/19 — £21,000 after £7,000 of allowable expenses. That rental income was never included on her Self Assessment return, and stayed missing from every year since, with income and costs both rising roughly 7% annually.
By 2022/23, her total unpaid tax comes to £59,409.
Her 2023/24 position is different, because a return for that year has already been filed. Since it’s within the amendment window (open until 31 January 2026), she can correct it directly without incurring additional late-filing penalties — though because the original payment deadline was 31 January 2025, late payment penalties and interest still apply.
Working through the penalty rates for the earlier years:
- Voluntary disclosure: total cost of £85,443
- Prompted disclosure: total cost of £94,354
A difference of £8,911 simply for disclosing before HMRC gets there first.
For 2023/24 specifically, if paid promptly:
- Late payment penalty (5% of £12,614): £631
- Interest on late payment: £355
Total tax, interest and penalty for 2023/24: £13,600
What If You Can’t Pay Everything Up Front?
HMRC expects payment in full at the point of disclosure — but that’s not always realistic, and it’s not a reason to delay. If you can’t cover the whole amount, the correct move is to contact HMRC’s Let Property Campaign helpline before you submit your disclosure or make any payment.
HMRC will want to understand your financial position to agree a realistic payment plan. Be ready to provide:
- Your disclosure reference number
- How and when you plan to pay what’s owed
- Your current income and outgoings, weekly or monthly
- What you own — property, vehicles, savings, investments
- What you owe — mortgages, loans, credit cards
Submitting a disclosure (or payment) before this conversation has happened, when you genuinely can’t pay in full, can create more problems than it solves.
The Bottom Line
HMRC’s enforcement capacity is only growing, and every month of delay adds interest, risk, and — if HMRC gets there first — significantly higher penalties. Whether the gap in your case was an honest oversight or something more deliberate, the Let Property Campaign rewards landlords who come forward on their own terms rather than waiting to be found.
Ready to find out what your voluntary disclosure would actually cost?