As a London small business grows, a familiar question arises sooner or later: should you hire an in-house accountant, or continue working with an external tax accountant on a retained basis instead? Both options can deliver excellent financial management, but they suit very different stages of business maturity, headcount and available budget. This comparison walks through the practical trade-offs in detail so you can make a decision based on your actual needs rather than assumptions about what "proper" businesses are supposed to do once they reach a certain size or turnover.
These considerations become even more pressing once you account for how quickly a small finance function can become a single point of failure inside an otherwise resilient business. Owners often discover the true cost of a gap only when it appears, whether that is a missed deadline, a badly timed absence, or a piece of specialist knowledge nobody in the building actually possesses. Weighing up the two models honestly, with real numbers rather than assumptions, tends to produce a far more confident decision than simply following whatever a peer business happens to have done.
The Case for an In-House Accountant
Bringing an accountant onto the payroll gives you a dedicated resource who understands your business intimately, sits in on meetings, and is available whenever a question arises during the ordinary working day without needing to be scheduled in advance. For larger SMEs with complex, high-volume finances, having someone permanently embedded within the team can genuinely speed up decision-making and reduce the friction of briefing an outsider every single time something changes. However, a single in-house hire, however capable and well-qualified, cannot realistically hold the same breadth of specialist knowledge across corporation tax, VAT, payroll legislation, R&D reliefs and capital gains that a dedicated external tax practice maintains across its whole team of specialists. Salary costs also extend well beyond gross pay once you factor in employer's National Insurance, pension contributions, sick leave, training and recruitment overheads that quietly accumulate across a full working year.
The Case for an External Tax Accountant
An external tax accountant, engaged on a monthly retainer or project basis, gives you access to a whole team of specialists rather than a single individual, often at a fraction of the cost of a full-time salary and its associated benefits package. You benefit from collective expertise built across many different client sectors, which is particularly valuable when facing an unusual situation such as an HMRC enquiry, a business restructuring, or a first-time VAT registration that your business has never had to navigate before on its own. External accountants also carry professional indemnity insurance and regulatory oversight, which adds a meaningful layer of protection that an informally hired in-house bookkeeper-turned-accountant may simply not carry. Many London firms find that ongoing business planning and financial advice from an external partner keeps strategic decisions grounded firmly in solid tax reality rather than in well-meaning guesswork.
Cost Comparison Across the Business Lifecycle
For a start-up or small business under roughly £1 million turnover, an in-house accountant is rarely cost-effective at all; the workload simply does not justify a full salary, and the role often ends up underused for much of the working week regardless of how capable the individual is. As turnover and transaction volume grow over time, the calculation naturally shifts, and at some point the hours needed from an external practice may approach or even exceed what a salaried role would cost on paper alone. There is no fixed threshold that applies neatly to every business, which is exactly why this decision deserves a proper cost comparison specific to your own numbers rather than a rule of thumb borrowed loosely from a competitor down the road.
- External accountants offer team-wide expertise rather than one person's knowledge
- In-house hires offer day-to-day availability and deep business familiarity
- Retainer arrangements scale up or down more easily than employment contracts
- Both routes require ongoing professional development to stay compliant
Flexibility and Scalability Over Time
One of the most underrated advantages of an external tax accountant is genuine flexibility. You can scale the relationship up during busy periods, such as year-end accounts preparation or a funding round, and scale back again during quieter months, paying only for what you genuinely need in that particular month. An employment contract simply does not flex in the same way; reducing an in-house accountant's hours or role is far more complicated, both administratively and in terms of morale within a small, close-knit team. For businesses with seasonal cash flow or an uncertain growth trajectory, this flexibility can often be the deciding factor when weighing up the two options carefully side by side.
Depth of Specialist Knowledge Available
Tax legislation changes frequently, and staying genuinely current across every relevant area is close to a full-time occupation in itself, even for a dedicated, conscientious professional. An external tax accountancy practice typically has partners and staff who each specialise in different areas, from personal tax through to corporate structuring, meaning your business benefits from a depth of knowledge that a single in-house hire simply cannot replicate alone however hard they try. This matters enormously when your business faces a genuinely complex situation, where getting specialist input on strategic financial planning can materially change the eventual outcome compared with a generalist's best guess made under time pressure and without proper support.
Continuity and Ongoing Business Risk
An often-overlooked risk of the in-house model is continuity of service. If your sole in-house accountant leaves, falls ill, or goes on extended leave, your entire financial function can grind to a halt at precisely the wrong moment, such as during a filing deadline or an unexpected cash flow crunch. External practices spread that risk across a wider team, so client work continues smoothly even if one individual happens to be unavailable for a period. This resilience is a genuine, practical advantage that becomes considerably more valuable the more your business depends on accurate, timely financial reporting to make confident everyday decisions.
Choosing the Right Model for Your Business
For most London small and medium businesses, particularly those under fifty employees, an external tax accountant tends to deliver better value, broader expertise and more flexibility than an in-house hire ever could achieve at that scale of operation. Larger, more complex organisations may eventually benefit from a hybrid model, combining an in-house finance manager for day-to-day operations with an external accountant handling tax strategy, statutory compliance and specialist advice as needed. The right structure ultimately depends on your size, complexity and growth ambitions, not on what merely looks impressive on an organisational chart to outsiders glancing in from a distance.
It is also worth considering how quickly your circumstances might change over the coming year or two, since that uncertainty itself favours flexibility over permanence in most cases. A business expecting rapid headcount growth, a funding round, or entry into a new market may find that committing to a single in-house salary locks in a cost structure that no longer matches reality within twelve months. An external relationship can absorb that kind of change far more gracefully, expanding or contracting scope without the formalities, notice periods and morale considerations that come with adjusting an employment contract.
The Bottom Line
There is no universally correct answer between an in-house accountant and an external tax accountant; the right choice depends squarely on your business's size, complexity and stage of growth. What matters most is making a deliberate decision based on cost, expertise and continuity, rather than defaulting to whichever option simply feels more traditional. For many London SMEs, an external tax accountant offers the strongest combination of specialist knowledge, flexibility and genuine value for money.
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Fred Michael & Co Ltd provides business planning and financial advice to help London businesses choose the right accounting service for them.