The Let Property Campaign: Disclosing Undeclared Rental Income to HMRC

Not every landlord with undeclared rental income got there deliberately. An inherited house that got let out rather than sold, a former home rented while living with a partner, a room let out and never mentioned on a return — the route in varies, but the position is the same: income HMRC doesn't know about, sitting there accumulating both tax and, eventually, interest and penalties. The Let Property Campaign exists precisely for this, and the terms for coming forward voluntarily are consistently and substantially better than the terms HMRC applies once it finds you first.

What the campaign actually is

The Let Property Campaign is an ongoing HMRC disclosure facility, not a time-limited amnesty, aimed specifically at individual landlords — not companies — with undeclared UK rental income. It covers UK residents letting property anywhere, non-UK residents letting UK property, single rental properties and large portfolios, long-term lets and furnished holiday lets, and applies equally whether the income was missed by an honest mistake or left off on purpose.

It does not cover income other than from letting property, and it isn't available if HMRC has already opened a compliance check or criminal investigation into your affairs covering the same period — at that point you're responding to an enquiry, not making a voluntary disclosure, and the terms on offer are materially worse.

Why HMRC usually gets there anyway

HMRC's Connect system cross-references data from the Land Registry, letting agents, deposit protection schemes, mortgage lenders (buy-to-let borrowing is a strong signal a property is let), council tax and electoral roll records, and, increasingly, data shared by short-let platforms. A property that shows up as let, mortgaged as a buy-to-let, or registered with a deposit scheme, but generates no matching rental income on a Self Assessment return, is exactly the pattern this system exists to surface. It typically isn't a question of if HMRC finds the mismatch, but when — and the terms on offer get worse the moment HMRC gets there before you do.

How the disclosure process works

The process runs in two stages:

• Notification. You tell HMRC you intend to make a disclosure under the Let Property Campaign. This starts a 90-day clock and, from that point, HMRC treats a subsequent compliance check on the same rental income as having been pre-empted by your notification — which matters for how any penalty is calculated.
• Disclosure and payment. Within 90 days, you calculate the tax, interest and any penalty due for each affected year, submit the disclosure, and pay what's owed (or agree a time-to-pay arrangement with HMRC if the amount can't be settled in full immediately).

Getting the calculation right matters: it isn't simply the missing rental income for each year, it's the correct net profit after allowable expenses, adjusted for any reliefs actually due — including, where relevant, correcting the position on jointly owned property under the rules covered in our guide to Form 17 and declaration of trust.

How the penalty is actually worked out

Penalties under the campaign are behaviour-based, not a flat percentage, and the two things that move the needle most are whether the disclosure was prompted or unprompted, and whether the original failure was careless or deliberate:

• Unprompted, careless — made before you had any reason to think HMRC suspected anything, where the failure to declare wasn't intentional. This attracts the lowest penalty band, and in a genuine reasonable-excuse case can be reduced to nil.
• Prompted, careless — made after you became aware HMRC might be looking, but still voluntary and still under the campaign. A materially higher penalty than the unprompted equivalent, but still well below what HMRC would charge on discovery.
• Deliberate — where income was knowingly left off. Higher again, and it can affect how many years HMRC goes back.

By contrast, income HMRC uncovers itself, rather than you disclosing, can attract penalties of up to 100% of the tax due for onshore matters, or up to 200% for income connected to offshore property or accounts — on top of the tax and interest, and with the added risk of a full compliance check into other years and other income sources at the same time.

How far back the disclosure needs to go

The number of years covered depends on how the failure is categorised, not on how long the property has been let:

• Careless behaviour — normally six years.
• Deliberate behaviour, or failure to notify HMRC of chargeability at all — up to twenty years.

For a landlord who has genuinely never registered for Self Assessment despite years of rental income, the twenty-year exposure is the default starting point HMRC applies, which is precisely why getting professional advice on how the disclosure is framed, before it's submitted, has a direct and often substantial effect on the final bill.

Common situations that end up here

The accidental route into an undeclared position is more common than the deliberate one:

• Inheriting a property and letting it out rather than selling, without realising the rental income needed reporting from day one.
• Moving in with a partner and letting a previous home, on the assumption that a small amount of rent "doesn't count" if it barely covers the mortgage.
• Letting a room or annexe informally, unaware that Rent-a-Room relief has a threshold and doesn't apply automatically to every letting arrangement.
• Non-resident landlords who assumed tax was fully settled by a letting agent withholding tax under the Non-Resident Landlords Scheme, when in fact a UK tax return was still required — see our guide on the Non-Resident Landlords Scheme for how that withholding actually interacts with Self Assessment.

If HMRC has already written to you

If a compliance check or "nudge letter" referencing rental property has already arrived, the Let Property Campaign is generally no longer the right route — you respond to that enquiry directly instead. That doesn't mean the position is hopeless; a well-handled response to an enquiry can still land at broadly similar penalty outcomes to a voluntary disclosure, particularly where you cooperate fully and disclose everything relevant immediately, rather than waiting for HMRC to ask each question in turn. See our guide on HMRC enquiries into property tax returns for how that process runs and what "full cooperation" actually looks like in practice.

Common questions

What is the Let Property Campaign?

An ongoing HMRC disclosure facility that lets individual landlords who haven't declared some or all of their rental income bring their tax affairs up to date on better terms than if HMRC discovers the shortfall first. It covers UK and non-resident landlords, single properties and portfolios, and applies whether the income was undeclared by mistake or deliberately.

How many years of undeclared rental income do I need to disclose?

Generally six years where the failure was careless, and up to twenty years where it was deliberate or you never registered for Self Assessment at all. Getting the categorisation right affects both the penalty and how many years of tax and interest are due.

What penalty will I pay under the Let Property Campaign?

Penalties are behaviour-based. An unprompted disclosure of a careless error attracts the lowest band, sometimes reduced to nil; a prompted disclosure is higher; both are substantially lower than the penalty HMRC would charge on discovering the same income itself, which can reach 100% of the tax due, or 200% for offshore matters.

How does HMRC find out about undeclared rental income?

HMRC's Connect system cross-references Land Registry records, letting agent data, deposit protection scheme registrations, mortgage lender data, council tax and electoral roll records, and platform data such as Airbnb, against Self Assessment returns. A mismatch between apparent rental activity and declared income is exactly what this system is built to flag.

This article is general information, not personal tax advice, and tax rules change. Your own position depends on facts we cannot see from here — please take advice before acting on anything above.

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