Employee Working a Second Job While Off Sick?

Updated 27 August 2026 by K3K Investigations

It is one of the most common workplace investigations in the UK — the employee signed off with a bad back or stress who is, colleagues whisper, labouring on a site, driving deliveries or running a market stall. And here is the pattern in the tribunal cases employers lose: it is almost never the employer who investigated that loses. It is the employer who accused first and looked for evidence afterwards.

If this suspicion has landed on your desk, the two mistakes available to you are doing nothing (and paying sick pay indefinitely while resentment spreads through the team) and moving too fast (and converting a dishonest employee into a successful unfair-dismissal claimant). This guide is the path between them.

Is working while off sick automatically misconduct?

No — and misunderstanding this is where employers come unstuck. A fit note is not house arrest. Someone signed off with workplace stress may be genuinely unable to work for you while being able, even encouraged, to stay active elsewhere; some fit notes expressly contemplate partial or alternative activity. A second job held openly for years is a different question from one concealed.

What is potentially gross misconduct is dishonesty: claiming to be too unwell to work while doing substantially similar work elsewhere, exaggerating incapacity, or breaching an express contractual bar on secondary employment. The distinction matters because it defines what your evidence must show — not merely "he was seen out and about", but activity genuinely inconsistent with the stated incapacity, reliably documented.

Why a tip-off and a screenshot are not enough

Most of these cases begin with a colleague's tip-off or a social-media sighting, and many employers stop gathering evidence right there. At tribunal, that position collapses quickly: screenshots are undated and contestable, a single sighting proves an afternoon rather than a pattern, and acting on gossip alone sits poorly with the requirement to carry out a reasonable investigation before dismissing. UK employment law does not demand proof beyond reasonable doubt — it demands a genuine belief on reasonable grounds after a reasonable investigation. The investigation is not an optional extra; it is the legal foundation of everything you do next.

What a lawful investigation looks like

Done professionally, an absence-abuse investigation is measured, documented and proportionate:

A documented justification first. Covert surveillance of an employee is lawful and tribunal-accepted where there is a legitimate aim, a reasonable suspicion, and no less intrusive way to resolve it — and where that reasoning is recorded before work begins. We prepare that with you; it is the paperwork that wins the case months later.
Surveillance in public places only, by professional operatives — timed, dated, continuous video of activity as it happens: the second workplace, the physical labour, the pattern across days rather than one ambiguous afternoon.
Open-source research done lawfully: publicly visible content, business listings, the second employer's public footprint. No befriending under false identities, no access to private accounts — evidence obtained that way undermines the case rather than building it.
Chain of custody and a report HR can rely on: exhibits, timeline, operative statements — prepared to the standard employment tribunals expect, ready to put to the employee in a fair disciplinary process.

The result cuts both ways, deliberately. Sometimes the footage shows a genuinely unwell employee doing exactly what their fit note allows — and that outcome protects you from a discrimination or unfair-dismissal claim you were sleepwalking into. Finding the truth is the product; the truth is sometimes "stand down".

What you receive, and what happens next

At the end you hold something no tip-off provides: days of documented, timed evidence that either substantiates the suspicion or disposes of it. From there the ordinary machinery applies — a fair disciplinary process, the evidence disclosed to the employee, their explanation heard. Employers who arrive at that meeting with professional surveillance evidence rarely arrive at tribunal at all; cases tend to resolve when the facts stop being arguable. One of ours ran six months of sick pay deep before the footage ended it in days — the full story is in The Six-Month Bad Back.

The cost, against the cost of waiting

Surveillance is charged per operative-day, and absence cases are usually short, pattern-focused deployments — the honest market rates are in our cost guide. Set that against the running total you are already paying: months of sick pay, cover costs, and the corrosive effect on the colleagues covering for someone they believe is working elsewhere. In most cases we see, the investigation costs less than the next few weeks of doing nothing.

Frequently asked questions

Is it legal to put an employee under surveillance in the UK?

Yes, within limits that professional investigators treat as non-negotiable: observation in public places, in pursuit of a documented legitimate aim, proportionate to a genuine suspicion that cannot be resolved less intrusively. Tribunals have repeatedly accepted covert surveillance evidence gathered on that footing — and criticised employers only where it was gratuitous or the process around it unfair.

Can we just check their social media instead?

You can look at what is public, and it is often a useful starting point — but rarely a sufficient finish. Public posts are undated snapshots, easily explained away, and accessing private content by subterfuge is unlawful and evidentially toxic. Treat social media as the reason to investigate properly, not the investigation.

What if the evidence shows they really are ill?

Then the investigation has done its job — quietly. You stop suspecting a genuine employee, no accusation is ever made, and you are protected from the claim that would have followed a wrongful one. This outcome is more common than employers expect, and we report it as plainly as the alternative.

Should we suspend the employee while we investigate?

Take employment-law advice on your specific facts — but as a rule, the great advantage of covert investigation is that nothing changes until you hold the evidence. Suspending first announces the suspicion, invites the behaviour to pause, and starts procedural clocks before you know what you are dealing with.

Paying sick pay to someone you suspect is working elsewhere? Describe the situation in a free confidential consultation — we will give you an honest read on whether surveillance is justified and a fixed quote if it is. Call 020 3343 7007 (24 hours) or book a call.