From 5 to 50 employees in the United Kingdom: an HR roadmap
Reviewed by Mellow Editorial Team, HR & payroll content team
Running a business with five employees is fundamentally different from running one with fifty. The HR and compliance obligations that were manageable informally at small scale become legally significant, administratively complex, and — if neglected — expensive as you grow.
What changes as you scale
At five employees, most founders handle HR personally. Contracts exist, payroll runs, and problems get dealt with as they arise. That works until it doesn't.
The shift between roughly ten and twenty-five employees is where informal systems tend to break. You are no longer close enough to every person to catch issues early. Decisions made inconsistently across the team create legal exposure. Processes that lived in someone's head need to be written down.
By fifty employees, you are operating what is effectively a small HR function whether you have named it that or not. Employment law applies fully, documentation matters, and the cost of a single tribunal claim — financial and operational — is real.
The compliance baseline you cannot skip
Certain obligations apply regardless of headcount, and they must be solid before you add anyone new.
Every employee needs a written statement of particulars on or before their first day. Under the Employment Rights Act 2025, day-one rights are strengthened further, so starting employment without proper documentation carries more risk than it did previously.
Payroll must run through HMRC's Real Time Information system. You submit a Full Payment Submission on or before each payday — not monthly, not in arrears. Employees pay income tax at 20% on earnings above the £12,570 personal allowance, 40% above the higher-rate threshold, and 45% above the additional-rate threshold. You pay employer National Insurance at 13.8% on qualifying earnings. Employee NI is 8% up to the upper earnings limit, then 2% above it. These figures apply in 2026/27.
Auto-enrolment pension obligations apply once you have eligible workers. You contribute a minimum of 3% of qualifying earnings; employees contribute 5%. Missing enrolment triggers escalating penalties from The Pensions Regulator.
Statutory annual leave is 5.6 weeks — 28 days including bank holidays for a standard five-day week. Statutory Sick Pay and statutory family-leave pay also apply. These are floors, not ceilings.
Building HR infrastructure at 10–25 employees
This is the phase where documentation stops being bureaucracy and starts being protection — for the business and for employees.
Write an employee handbook. It does not need to be long, but it needs to cover disciplinary and grievance procedures, sickness absence, equality and dignity at work, and any policies specific to how you operate (remote work, expenses, data handling). Consistent policies mean consistent decisions, and consistent decisions are much harder to challenge.
Set up a basic HR system. A spreadsheet tracking holidays, absences and employment dates will eventually fail you. Even a simple HR platform gives you an audit trail, which matters if a dispute arises. It also makes producing your P60s by 31 May and P11Ds by 6 July significantly less painful.
Define roles properly. As you hire beyond the founder's direct orbit, job descriptions and reporting lines prevent the ambiguity that causes grievances. They also make performance conversations more objective.
Managing compliance at 25–50 employees
Beyond twenty-five employees, several things shift in practice even if the law itself does not draw a hard line at that number.
Disciplinary and grievance cases become more frequent simply by probability. You need managers trained to handle them correctly — following the Acas Code of Practice is not optional if you want to defend a tribunal claim. Unfair dismissal claims can arise after two years of service; constructive dismissal claims can arise from day one.
Equality Act obligations become operationally significant. With a larger workforce, you need to think actively about recruitment practices, reasonable adjustments, and how promotion decisions are made and recorded. Pay equity is worth auditing before it becomes a complaint.
At this scale, payroll complexity increases. You are likely managing multiple pay grades, possibly part-time and variable-hours workers, enhanced contractual entitlements layered on top of statutory minimums, and potentially benefits such as private medical or cycle-to-work schemes that each carry their own reporting obligations. If you are running payroll in-house, ensure your processes can handle this. If you are using a bureau or a platform that runs payroll across multiple countries, make sure your internal records are clean enough to feed it accurately.
When to hire dedicated HR resource
There is no universal headcount trigger, but a useful test is this: if a significant employment decision — a dismissal, a restructure, a grievance — would be handled without anyone in the business having employment law knowledge, you have a gap.
Some businesses bring in a part-time HR professional or fractional HR director at around twenty employees. Others use an employment law advisory service as a first step. What matters is that someone with relevant knowledge is involved before a decision is made, not after a claim has been filed.
At fifty employees, an in-house HR lead — even at 0.5 FTE — typically pays for itself through avoided claims, reduced manager time on people issues, and more consistent hiring.
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