Telling HMRC About Undeclared Income: Voluntary Disclosure for Trade Businesses (UK Guide)

What Is a Voluntary Disclosure?

A voluntary disclosure is when you proactively tell HMRC that you've under-declared tax in the past, calculate what you owe, and pay it — including interest and a penalty — before HMRC opens an enquiry into you. You're coming forward of your own accord rather than waiting to be found out.

The key word is "unprompted". In HMRC's language, a disclosure is unprompted if you make it at a time when you had no reason to believe HMRC had discovered, or was about to discover, the error. A disclosure is prompted if you only come forward after HMRC has already started asking questions or has written to you about it. As you'll see below, the difference between the two has a huge effect on the penalty you pay.

Why It's Far Better Than Waiting to Be Caught

Coming forward voluntarily is not just the honest thing to do — it is, on every practical measure, the cheaper and safer route.

• Much lower penalties. An unprompted disclosure attracts a far smaller penalty than a prompted one. For careless errors that have been put right voluntarily, the penalty can be reduced to zero; for deliberate behaviour disclosed unprompted, the reductions are still substantial.
• It shows reasonable behaviour. Coming forward demonstrates that you're trying to put things right, which HMRC takes into account when deciding how to categorise your behaviour and how hard to push.
• It heads off a full investigation. A voluntary disclosure is generally dealt with as a contained process. Waiting to be caught can trigger a full enquiry that crawls over every part of your business for years.
• It avoids COP9 and prosecution. For serious or deliberate cases, coming forward through the right channel can take criminal prosecution off the table. Being caught for deliberate, concealed evasion can lead to a Code of Practice 9 (COP9) fraud investigation and, in the worst cases, prosecution.

Put simply: the cost of fixing it yourself is almost always a fraction of the cost of HMRC fixing it for you.

The Disclosure Routes

HMRC runs several disclosure facilities, and the right one depends on the type of income involved and whether the behaviour was innocent, careless or deliberate. For most trade businesses, it comes down to three.

1. The Digital Disclosure Service (DDS)

The DDS is HMRC's general-purpose disclosure facility. It covers most income tax, Capital Gains Tax and Corporation Tax errors — so it's the route most sole traders and small Ltd companies use for forgotten cash jobs, missed income, over-claimed expenses or undeclared side work. You notify HMRC of your intention to disclose online, and you're then given time to work out and pay what you owe.

2. The Let Property Campaign

If part of your undeclared income is rental income — for example you let out a property and never declared the profit — the Let Property Campaign is the dedicated route for residential landlords. Many tradespeople own a rental property alongside the business; if that's where the gap is, this is the facility to use.

3. The Contractual Disclosure Facility (COP9)

COP9 is for deliberate behaviour — tax fraud. Under the Contractual Disclosure Facility you admit that your conduct was deliberate in exchange for HMRC's undertaking not to pursue a criminal prosecution for the disclosed conduct. It is a serious, formal process and you should never enter it without specialist professional representation. If your undeclared income was the result of deliberately hiding cash jobs or knowingly suppressing takings, this — not the DDS — is likely the correct route, and advice is essential before you act.

Quick Reference: Which Disclosure Route?

How the Process Works

Although the routes differ, the shape of a voluntary disclosure is broadly the same:

• Notify. You tell HMRC you intend to make a disclosure. This registers your intention and, importantly, fixes the point at which you came forward.
• Calculate. Once you've notified, you usually get around 90 days to work out the tax owed across all the relevant years, plus the interest and the penalty.
• Disclose and pay. Within that window you submit the disclosure — your figures and an offer of what you owe — and pay the tax, interest and penalty.

The 90-day period is generous but it goes quickly when you're reconstructing several years of records. Start pulling together bank statements, invoices and old returns as soon as you notify — don't wait until the deadline is near.

How Far Back Do You Have to Go?

How many years you need to include depends on why the error happened. HMRC works to different time limits according to behaviour:

• 4 years where you took reasonable care but made an innocent error.
• 6 years where the error was careless — you didn't take enough care, but it wasn't deliberate.
• Up to 20 years where the behaviour was deliberate.

Being honest with yourself about which category applies matters. Understating the number of years to keep the bill down is exactly the kind of thing that can turn a careless case into a deliberate one in HMRC's eyes if it later unravels.

How Penalties Are Reduced

Penalties are calculated as a percentage of the extra tax due, and the percentage depends on two things: how serious the behaviour was, and how much you cooperate. HMRC reduces the penalty according to the quality of your disclosure, measured across three areas:

• Telling — admitting the error and explaining how and why it happened.
• Helping — doing the work to quantify what's owed, rather than leaving HMRC to dig.
• Giving access — providing records and answering questions promptly.

The more you do across all three, the lower the penalty. And on top of that, an unprompted disclosure is rewarded with a bigger reduction than a prompted one. This is why coming forward early and cooperating fully is worth real money.

Prompted vs Unprompted: The Penalty Difference

These figures are indicative of how the system works rather than a quote for your case — the exact percentage depends on your specific circumstances and the quality of your cooperation. The pattern, though, is consistent: coming forward unprompted and helping fully can cut the penalty dramatically, sometimes to nothing.

Paying What You Owe

When you make the disclosure you're expected to pay the tax, interest and penalty. For many trade businesses that have built up several years of undeclared income, the total can be a significant sum landing all at once.

If you genuinely can't pay it all in one go, you can ask HMRC for a Time to Pay arrangement — a structured instalment plan that spreads the bill over a manageable period. You'll need to show your figures and explain what you can realistically afford. The important thing is that an inability to pay immediately is not a reason to avoid disclosing; it's something HMRC will work with you on, but only once you've come forward.

The Risks of Not Disclosing

Hoping the problem goes away is the most expensive option of all. HMRC's data capabilities have moved on enormously:

• HMRC Connect. HMRC's Connect system pulls data from banks, payment processors, online marketplaces, Land Registry, the DVLA and dozens of other sources, cross-references it against your declared income, and flags mismatches. Cash jobs paid by bank transfer, card payments and online listings all leave a trail.
• Higher penalties. If HMRC opens the enquiry, your disclosure becomes prompted and the minimum penalties jump — the very reductions you could have earned by coming forward are lost.
• Naming. HMRC can publish the details of deliberate defaulters whose evaded tax is above a threshold, putting your name and business on a public list.
• Prosecution. In the most serious deliberate cases, criminal prosecution is possible. Coming forward through the right channel is what keeps that risk off the table.

Why Professional Advice Matters First

For a straightforward careless error, the DDS is designed to be usable without an accountant — but even then, an adviser will help you scope the right number of years, categorise the behaviour correctly and present the disclosure in a way that maximises the penalty reduction. The risk of getting the categorisation wrong, or of accidentally understating the disclosure, is real.

For anything that might be deliberate, professional advice isn't optional — it's essential. The choice between the DDS and COP9, and how you frame an admission of deliberate behaviour, has consequences that include whether prosecution stays on the table. Speak to a tax adviser or accountant who handles disclosures before you contact HMRC. A short conversation up front can change the entire outcome.

The Bottom Line

If you've realised your trade business has under-declared tax, the worst thing you can do is nothing. A voluntary, unprompted disclosure means lower penalties, no full investigation, and the matter put behind you. Waiting to be caught means higher penalties, the possibility of naming, and — for serious cases — the risk of prosecution. Get your records in order, take advice on the right route, and come forward. It is almost always cheaper, calmer and cleaner than the alternative.

This article is general information for UK trade businesses and is not personal tax advice. Always check your own position with a qualified accountant or tax adviser before making a disclosure to HMRC.