In the UK, Self Assessment is a tax system under which taxpayers are required to declare their own income and tax position. Unlike the PAYE system—where tax is calculated and deducted by an employer—Self Assessment requires individuals to calculate, report, and pay their tax based on their own circumstances.

The core principle of Self Assessment is clear: the taxpayer bears ultimate legal responsibility.

Regardless of whether you appoint someone else to assist with your tax return—including an accountant or tax adviser—the legal responsibility always remains with you. Even if you have paid a professional fee, if your return contains errors, omissions, or is submitted late, HMRC will pursue the taxpayer, not the third party acting on your behalf.

HMRC’s official guidance also clearly states that taxpayers must ensure their returns are accurate and complete, and that reasonable steps must be taken to verify the information submitted.

Numerous tax cases reflect the same principle: even where a taxpayer follows an accountant’s advice or allows an agent to submit the Self Assessment return, responsibility still rests with the taxpayer if the return is incorrect. In some judicial decisions, judges have explicitly stated that taxpayers must be “responsible for their understanding of the facts and the law,” meaning that the involvement of a third party does not transfer legal responsibility.

Why Do Incorrect SA100 Filings Still Occur So Frequently in Practice?

This allocation of legal responsibility also shapes how the UK tax services market operates in reality. Because ultimate legal responsibility under the Self Assessment system rests with the taxpayer—not the person submitting the return—there are indeed certain service models in the market that focus not on reviewing or assessing the reasonableness of the figures, but simply on submitting whatever numbers the client provides.

In such cases, the accountant’s role becomes largely technical—executing the submission—rather than acting as a reviewer or adviser exercising professional judgement. As long as the information is supplied by the client, it is accepted at face value, with limited challenge, verification, or warning of potential risks. These services are often low-cost and cater to taxpayers seeking a “quick and cheap” way to complete their tax return.

However, under the UK Self Assessment legal framework, when problems arise, the consequences are borne not by the service provider, but by the taxpayer themselves.

Real Case 1: Penalties Due to an Accountant’s Failure to Submit a Return

A taxpayer instructed an accountant to set up personal details within HMRC’s system and handle their Self Assessment filing. Due to an error made when setting the address, the taxpayer did not receive penalty notices or payment reminders issued by HMRC. HMRC subsequently imposed penalties and interest under the Self Assessment regime.

Based on the taxpayer’s account and related community discussions, HMRC made it clear that regardless of third-party involvement, the penalties and consequences remained the taxpayer’s responsibility.
(Source: Reddit / LegalAdviceUK)

Real Case 2: Accumulated Penalties Due to Missed Filing Obligations

Another taxpayer failed to submit annual Self Assessment returns for several consecutive years due to a lack of understanding of their tax obligations. Even though all taxes due had been fully paid, HMRC imposed automatic penalties, daily late-filing penalties, and interest for failure to submit the required returns, resulting in total penalties amounting to several thousand pounds.

This situation is not uncommon among new migrants or individuals unfamiliar with the UK tax system, often due to a lack of proper guidance or the mistaken belief that filing was not required.
(Source: Reddit / UKPersonalFinance)

Why Does Self Assessment Place Such Emphasis on Taxpayer Responsibility?

Under UK tax law, Self Assessment is designed as a system in which taxpayers assess and declare their own tax liabilities. HMRC expects taxpayers to act reasonably and with due care, ensuring that returns are accurate, complete, and justifiable. Where submitted information is incorrect or incomplete, HMRC may impose penalties under its penalty regime for careless or inaccurate returns.

In other words, paying an accountant does not mean legal responsibility can be transferred. Under the Self Assessment system, the taxpayer always remains the final person responsible.

Professional Guidance: How to Reduce Tax Filing Risks

• Understand the nature of Self Assessment responsibility
  You must understand what you are declaring and review whether the submitted information is complete and accurate.
• Choose a tax adviser with relevant experience and professional qualifications
  Price should not be the sole deciding factor. Professional judgement and proper review are critical in avoiding errors.
• Maintain proper income and expense records
  Good records not only support accurate filing but are essential in the event of an HMRC enquiry.
• Refer to HMRC’s official guidance when in doubt
  If you are unsure about your filing obligations, seek confirmation rather than relying on a single informal opinion.
• We do not recommend tax services that do not review or verify the underlying documents.In reality, there are service models within the UK tax market that focus solely on submitting information based on client instructions, without assessing whether the figures are reasonable or complete.
• Such services often appear efficient, streamlined, and low-cost—but low fees usually have a reason.The reason is that the tax return itself has not undergone any substantive review. Under the Self Assessment system, when issues arise, the consequences are borne by the taxpayer—not the party that submitted the return.

Our Position in Elaga Accountancy: Review, Judgement, and Responsibility

Under the UK Self Assessment system, taxpayers bear ultimate legal responsibility. For this reason, choosing an accountant with genuine UK tax experience—one who is willing to review and apply professional judgement to your return—is essential.

Our team in Elaga has received professional training in the UK and is familiar with both the UK tax system and HMRC’s practical processes. We do not merely understand the rules—we understand how they operate in reality. Over the years, we have accumulated extensive experience covering personal tax, Self Assessment, overseas income, rental income, and more complex tax situations, enabling us to review each return from the taxpayer’s perspective.

Unlike service models that simply submit client-provided data without substantive review, we carefully examine documentation, raise questions proactively, test logic and consistency, and ensure that every return complies with UK tax law and HMRC requirements. We believe the true value of professional work lies not in speed, but in accuracy and responsibility.

Because the ultimate consequences under Self Assessment rest with the taxpayer, our accountants in Elaga always committed to providing services built on care, transparency, and professional judgement—ensuring that every return can withstand scrutiny.

Responsibility and Peace of Mind Go Hand in Hand

Self Assessment is designed to place responsibility for tax reporting on the taxpayer. While professional assistance is important, paying a fee does not equate to transferring risk. Only by understanding the system and reviewing each element of a return can taxpayers truly avoid penalties and adverse consequences arising from mistakes or omissions.

Seek Accountant's Help for Your Tax Return

Given the October rush, it’s more important than ever to have reliable support. If you’re unsure about whether you need to file, how to report specific income types, or you want peace of mind your return is done correctly and on time — Elaga Accountancy can help.

We’ll handle your registration, confirm your UTR, prepare your return, and send it on your behalf so you’re compliant and penalty-free.

Don’t wait until the last minute and risk being caught out. Let us take the stress away — you’ll know your affairs are in order, and you’re meeting your legal duty to file and pay.

***Contact us to learn more.

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