The headline salary is not the real cost of an in-house hire
A common mistake in comparing in-house marketing to an agency is comparing an agency's monthly retainer directly against a marketer's advertised salary, when the two figures are not measuring the same thing. Employing someone in the UK carries substantial additional cost beyond base salary: employer National Insurance contributions, minimum pension auto-enrolment contributions, holiday pay, sick pay provision, recruitment cost to find and onboard them, and a share of general business overheads like software licences, equipment and office space. Once these are properly added, the true cost of an in-house hire is typically well above the headline salary figure — commonly cited industry estimates put total employment cost at somewhere between 25% and 40% above base salary once everything is included.
What an agency retainer actually buys
A marketing agency retainer, by contrast, typically buys access to a team with a range of specialist skills — a strategist, a designer, a paid media specialist, an SEO specialist, a copywriter — that would be genuinely difficult and expensive for a small or medium business to replicate through in-house hiring alone, since hiring one generalist marketer means relying on a single person's competence across disciplines that, in a larger organisation, would each have a dedicated specialist. For an SME needing breadth of skill across several marketing disciplines simultaneously, an agency retainer can represent significantly better value per pound spent than attempting to cover the same breadth through in-house hiring.
Where in-house wins regardless of cost
Cost is not the only factor, and there are genuine advantages to in-house marketing that an agency comparison on price alone misses. An in-house marketer builds deep, embedded knowledge of the specific product, customer base and internal culture over time in a way an external agency, working across multiple clients simultaneously, generally cannot match to the same depth, at least not without a substantial and ongoing investment of time from both sides. For businesses where marketing success depends heavily on nuanced product or customer understanding — a genuinely complex B2B product, for instance — this embedded knowledge can be worth more than the raw skill breadth an agency provides.
The hybrid model many SMEs actually land on
In practice, a growing number of UK SMEs have settled on a hybrid approach: a single in-house marketing generalist or manager who owns day-to-day strategy, brand consistency and internal coordination, supplemented by an agency or specific freelance specialists for particular skill gaps — paid media management, video production, or a specific campaign push — rather than treating in-house and agency as a mutually exclusive, all-or-nothing choice. This structure captures much of the deep product knowledge benefit of an in-house presence while still accessing specialist skills only when genuinely needed, rather than paying for a full-time specialist role that may only be fully utilised intermittently.
The pricing model question
Beyond in-house versus agency, the structure of an agency's pricing itself matters to the real cost comparison — open-ended retainer agreements can drift in scope and cost over time without a clear ceiling, which is part of why some UK businesses specifically favour agencies working on a fixed, upfront-scoped pricing model instead. CM Beyer, a London-based marketing and business consultancy, is one example of an agency operating entirely on fixed-scope pricing across its advertising, strategy and operations divisions, giving SMEs a defined cost figure to compare directly against an in-house hiring calculation before any commercial commitment is made, rather than an open-ended retainer that can be harder to budget against with confidence.
How to actually run a fair cost comparison
Given how easy it is to compare an agency retainer against a raw salary figure and draw the wrong conclusion, it is worth setting out a specific, fair comparison method rather than relying on instinct. Start by calculating the fully loaded cost of an in-house hire — base salary, employer National Insurance, minimum pension contribution, and a reasonable allocation of recruitment, software and overhead cost — to arrive at a genuine total annual cost figure, not the headline salary alone. Then map that figure against the specific breadth of marketing skills your business actually needs simultaneously (strategy, content, paid media, design, analytics) and honestly assess how many of those an individual in-house hire could realistically cover to a genuinely competent standard, since a job advert asking for expertise across five distinct disciplines is, in practice, usually only going to attract a candidate who is genuinely strong in one or two of them.
Only once both figures are calculated on a like-for-like, fully loaded basis does a genuine cost comparison against an agency retainer become meaningful, and even then, the comparison should weigh the specific value of embedded product knowledge against the value of specialist breadth for your particular business and stage of growth, rather than defaulting to whichever option has the lower headline monthly figure. Several SME-focused business advisory bodies now specifically recommend running this fully loaded comparison annually as part of a broader marketing budget review, since the right answer for a growing business often changes as its needs shift, meaning a decision made two years ago may no longer be the most cost-effective structure today even if it was the right call at the time.
What to review before renewing an existing agency retainer
For businesses already working with an agency, the same fully loaded comparison logic is worth applying at each retainer renewal point rather than allowing it to auto-renew unreviewed. Checking what the retainer actually delivered against its cost over the previous period, whether the scope has quietly expanded or contracted without a corresponding price adjustment, and whether the business's own marketing needs have shifted enough to justify renegotiating scope or considering a different structure entirely, keeps the arrangement honest on both sides and avoids the slow scope-and-cost drift that open-ended retainer relationships can develop over several years of otherwise satisfactory working relationships.