When people talk about “red flags” on a tax return, it can sound as if HMRC uses one simple checklist and automatically opens an enquiry the moment something looks a bit unusual. Real life is not quite like that.
HMRC can check any tax return to make sure it is accurate and complete. Some checks are prompted by risk factors, while others can be random. In other words, a question from HMRC does not automatically mean you have done something wrong. What matters most is whether your return is complete, your figures make sense, and your records support what you have filed.
That is why the best way to reduce risk is not to panic about hidden triggers. It is to build a return that is tidy, consistent and backed by proper records.
At Asmat, that practical, straightforward approach is exactly what comes across on the website. The firm supports clients with tax returns, bookkeeping, VAT returns, company accounts, payroll services and wider accountancy services, with support aimed at sole traders, limited companies, partnerships, LLPs, contractors and small businesses across the UK.
Why HMRC asks questions in the first place
HMRC’s job is to collect the right amount of tax, not simply to catch people out. Checks usually happen because something looks incomplete, inconsistent or unusually high or low compared with the rest of the return.
HMRC gives examples of things that may prompt a compliance check, such as figures that seem wrong, a large VAT refund claim when turnover is low, or a small amount of declared tax when turnover is high. That tells you something useful straight away: many “red flags” are really about whether the numbers look believable when taken as a whole.
So if you want to reduce the chances of HMRC asking questions, the goal is simple. Your income, expenses, drawings, salary, dividends, VAT filings, payroll records and accounts should all tell the same story.
1. Income that looks too low for the business activity shown
One of the clearest ways to attract attention is to file a return that suggests your business is active, but your declared income looks surprisingly low.
That could mean:
- turnover that seems out of step with your industry or previous years
- profits that suddenly collapse without a clear reason
- low personal income while business spending or lifestyle withdrawals appear much higher
- a return that does not fit with information already supplied elsewhere
Of course, there can be perfectly sensible explanations. You may have had a poor year, lost a contract, invested heavily in the business, taken time off, or gone through a major transition. None of that is a problem if the records are there and the explanation is clear.
This is where good financial reports and current bookkeeping make a real difference. If your records are up to date, it is far easier to explain why profit dropped, why margins changed, or why cash flow looked different this year.
2. Missing income from side work, property or mixed sources
A lot of tax problems begin with income that felt too small, too casual or too irregular to matter. That might be freelance work, consulting, subcontracting, a few months of rental income, online sales, or additional work alongside employment.
HMRC expects taxable income to be reported properly, even when it comes from several different sources. There are tax-free allowances for some trading and property income, but they are limited and depend on your circumstances. For example, the trading allowance and property allowance are each up to £1,000 a year, and they do not apply in every situation.
For landlords, HMRC says you may need to complete a tax return if your gross property income is more than £10,000 or your profit is more than £2,500 after allowable expenses.
This is why side income is such a common issue. People often assume that if it is not their “main” income, it is not especially important. But if HMRC can see evidence of income that does not appear properly on the return, that can quickly lead to questions.
If you earn from more than one source, it helps to get advice built around the right structure from the start, whether that means support for sole trader accounting, contractors, limited company accountants or partnership accountants.
3. Expenses that look personal rather than business-related
This is one of the biggest risk areas on any tax return.
HMRC’s rule for self-employed expenses is straightforward: you can only claim costs that are wholly and exclusively for the purposes of the trade. If something has both personal and business use, only the business part is allowable. You must also keep records to support what you have claimed.
The problem is that real life is rarely neat. Many expenses sit in a grey area, such as:
- home office costs
- mobile phone bills
- motor expenses
- travel mixed with personal time
- meals and entertaining
- clothing
- software or subscriptions used partly for private purposes
That is where trouble starts. A claim may feel reasonable, but if you cannot show how you calculated the business portion, HMRC may challenge it.
Another common issue is misunderstanding the difference between routine expenses and capital items, or claiming full finance repayments rather than only the elements that are actually allowable. The more mixed or unusual the expense looks, the more important the supporting explanation becomes.
A clean process helps here. Use a separate business bank account where possible. Keep receipts. Add notes to unusual transactions. Review categories before the return is filed. If something looks borderline, get it checked rather than assuming it will be fine.
4. Returns that do not match other HMRC filings
A tax return does not sit on its own. HMRC may compare it with other information it already holds, including VAT returns, payroll submissions, company tax information and other records connected with your affairs.
That means inconsistencies can cause problems, even when each figure was entered with good intentions.
Examples include:
- turnover on your tax return that does not fit with your VAT profile
- salary figures that do not align with payroll submissions
- income taken from a company that does not make sense alongside the company accounts
- property or business income that looks incomplete compared with other filings
This is one of the strongest reasons to keep your compliance work joined up. When your company accounts, VAT returns, payroll services and tax return are reviewed together, mismatches are much easier to spot before HMRC sees them.
5. Filing late or rushing the return at the last minute
Late filing does not just create penalties. It also increases the risk of mistakes.
For online Self Assessment returns, the deadline is 31 January following the end of the tax year. HMRC says that if you miss the filing deadline, an automatic late filing penalty usually applies. Payment deadlines also matter, because late-paid tax can trigger interest and additional penalties.
In practice, a rushed return is often a messy return. Receipts are missing, figures are estimated badly, income gets overlooked, and unusual items are not reviewed properly.
A much better approach is to treat January as the end of the process, not the moment you begin thinking about it. If your records are kept current throughout the year, the tax return becomes a final review rather than a last-minute scramble.
That is especially important if you are juggling payroll, VAT, CIS or company compliance at the same time. Support from small business accountants or QuickBooks accountants can help keep your numbers moving in the right direction all year, rather than leaving everything until the deadline.
6. Poor records or no evidence behind the figures
This is one of the most avoidable reasons for HMRC questions.
If you are in business, HMRC says you must keep records that allow you to complete your return accurately. Self-employed taxpayers generally need to keep records for at least 5 years after the 31 January submission deadline for the relevant tax year. HMRC can also charge penalties if records are not accurate, complete and readable.
Poor records create problems in 2 ways.
First, they are more likely to make mistakes. If invoices are missing, bank transactions are not reconciled, or receipts are incomplete, it becomes much easier to understate income or overstate expenses.
Second, they make it harder to defend the return later. You may know an expense was genuine, but if you cannot show what it was for, when it happened, and how it relates to the business, you are in a weaker position.
HMRC also says that if you took reasonable care to get things right, it will not charge a penalty for inaccuracy. Examples of reasonable care include keeping accurate records and checking with a tax adviser or HMRC when you are unsure.
That means good records do not just help you file the return. They also help protect you if the return is ever checked.
7. Using guesswork instead of proper explanations
Some business owners worry that anything unusual will automatically cause trouble, so they try to smooth the figures or make rough assumptions. That usually creates more risk, not less.
If you genuinely do not have a final figure, HMRC does allow provisional or estimated figures in some cases, but you are expected to make that clear and explain it in the return.
That matters because honest explanation is far better than unexplained inconsistency. If your income changed sharply, say why. If a large repair bill hit your rental profit, make sure the records show it. If you started or stopped trading part way through the year, make sure the return reflects that properly.
HMRC is generally more concerned with whether the return is correct and transparently prepared than with whether every year looks perfectly smooth.
8. Claiming reliefs or tax positions you do not fully understand
Another common problem is claiming something because it sounded available, without checking whether it actually applies.
That can happen with:
- use of home claims
- travel rules
- rental expense treatment
- allowances for small trading or property income
- capital allowances
- contractor or subcontractor tax positions
The issue is not that reliefs are suspicious in themselves. The issue is claiming them carelessly, calculating them badly, or putting them in the wrong place.
This is especially important if you operate through a company or have more than one income stream. A personal return often links back to business records, payroll, dividends, company tax and accounts. The more moving parts you have, the more valuable it is to have them reviewed together.
9. Falling behind with digital record-keeping
Digital compliance is becoming more important, not less.
HMRC says Making Tax Digital for Income Tax will apply from 6 April 2026 to sole traders and landlords with qualifying income over £50,000, from 6 April 2027 for those over £30,000, and from 6 April 2028 for those over £20,000. Those within scope will need compatible software to keep digital records and send updates to HMRC.
This does not mean manual records are automatically wrong today. But it does mean weak systems are becoming harder to justify. If records are scattered across paper notes, spreadsheets, personal accounts and half-complete apps, errors become more likely.
Getting organised now can reduce future risk. Better software, regular reconciliations and cleaner records make returns easier to prepare and easier to defend.
How to make your tax return look low-risk
Reducing risk is usually less about tax tricks and more about basic discipline.
Keep your books up to date throughout the year. Separate business and personal spending wherever possible. Make sure all income streams are captured. Review unusual expenses before they go into the return. Check that your tax return matches your accounts, payroll and VAT position. File early enough to think clearly. And if you are unsure, ask before the return is submitted.
That last point matters. HMRC’s own guidance makes clear that reasonable care includes checking with a tax adviser or HMRC if you are uncertain.
Final thoughts
Most HMRC questions do not start because a taxpayer hit some mysterious secret trigger. They start because the return does not add up properly, the records are weak, or key details have been missed.
The good news is that these risks are usually manageable. If your records are clean, your income is fully reported, your expense claims are sensible, and your filings are consistent, you are already in a much stronger position.
If you want your tax affairs handled with less stress and fewer surprises, Asmat can help with tax returns, bookkeeping, VAT returns, company accounts, payroll services and broader accountancy support. You can contact the team to get your records in better shape and make your next tax return feel far more straightforward.
