Employee Working a Second Job While Off Sick?

Updated 5 October 2026 by Investigation Bureau

This is among the most common workplace investigations in the UK. An employee is signed off with a bad back or with stress, and colleagues are whispering that the same person is labouring on a building site, driving deliveries or running a market stall. In the tribunal cases that employers lose there is a pattern. The loser is rarely the employer who investigated. It is the employer who made the accusation first and went looking for evidence afterwards.

If this suspicion has reached your desk, two mistakes are open to you. One is to do nothing, pay sick pay indefinitely and watch resentment spread through the team. The other is to move too fast and turn a dishonest employee into a successful unfair dismissal claimant. This guide describes the route between the two.

Is it automatically misconduct to work while off sick?

No, and employers who misunderstand this come unstuck. A fit note is not house arrest. Someone signed off with workplace stress may be truly unable to work for you and still be able, even encouraged, to keep active elsewhere. Some fit notes expressly allow for partial or alternative activity. A second job that has been held openly for years also raises a different question from one that was concealed.

What can amount to gross misconduct is dishonesty: saying you are too unwell to work while doing substantially similar work somewhere else, exaggerating incapacity, or breaking an express term of the contract that bars secondary employment. The distinction matters because it sets what your evidence has to show. "Seen out and about" is not enough. The evidence must show activity that is truly inconsistent with the stated incapacity, and it must be reliably documented.

Why a tip-off and a screenshot are not enough

Most of these cases start with a tip-off from a colleague or a sighting on social media, and many employers stop gathering evidence at that point. In front of a tribunal that position falls apart quickly. Screenshots are undated and open to dispute. One sighting proves an afternoon, not a pattern. And acting on gossip alone fits badly with the duty to carry out a reasonable investigation before dismissing. UK employment law does not ask for proof beyond reasonable doubt. It asks for a genuine belief, on reasonable grounds, after a reasonable investigation. The investigation is not an optional extra. Everything you do next rests on it.

What a lawful investigation looks like

Carried out professionally, an absence investigation is measured, documented and proportionate.

A documented justification comes first. Covert surveillance of an employee is lawful, and accepted by tribunals, where there is a legitimate aim, a reasonable suspicion and no less intrusive way to settle the matter, and where that reasoning is written down before the work starts. We prepare that record with you. It is the paperwork that wins the case months later.
Surveillance in public places only. Professional operatives record timed, dated, continuous video of activity as it happens: the second workplace, the physical labour, the pattern over several days and not one ambiguous afternoon.
Open-source research done lawfully. Publicly visible content, business listings and the public footprint of the second employer. No befriending under a false identity and no access to private accounts. Evidence obtained like that weakens the case it was meant to build.
Chain of custody and a report HR can rely on. Exhibits, a timeline and operative statements, prepared to the standard employment tribunals expect and ready to be put to the employee in a fair disciplinary process.

The result can go either way, and that is by design. Sometimes the footage shows an employee who really is unwell doing exactly what the fit note permits. That outcome protects you from a discrimination or unfair dismissal claim you were about to walk into. What you are paying for is the truth, and sometimes the truth is "stand down".

What you receive, and what happens next

At the end you hold something a tip-off can never give you: several days of documented, timed evidence that either supports the suspicion or disposes of it. After that the ordinary process applies. You run a fair disciplinary procedure, disclose the evidence to the employee and hear their explanation. An employer who comes to that meeting with professional surveillance evidence seldom ends up at a tribunal, because cases tend to settle once the facts can no longer be argued over. Our illustrative case story, a workplace absence investigation, shows how a long-running absence case can be brought to an end by a few days of footage.

The cost, set against the cost of waiting

Surveillance is charged per operative per day, and absence cases are usually short deployments aimed at establishing a pattern. Honest market rates are set out in our cost guide. Compare that with the bill you are already running up: months of sick pay, the cost of cover, and the corrosive effect on colleagues who are covering for someone they believe is working elsewhere. Often the investigation costs less than a few more weeks of doing nothing.

Frequently asked questions

Is surveillance of an employee legal in the UK?

Yes, within limits a professional investigator treats as fixed: observation in public places, for a documented legitimate aim, and proportionate to a genuine suspicion that cannot be settled in a less intrusive way. Tribunals have repeatedly accepted covert surveillance evidence gathered on that footing. Their criticism has been reserved for employers whose surveillance was gratuitous or whose surrounding process was unfair.

Could we simply check their social media instead?

You may look at what is public, and it is often a useful place to start. It is rarely enough to finish on. Public posts are undated snapshots that are easy to explain away, and getting at private content by subterfuge is unlawful and ruins the evidence. Treat social media as the reason to investigate properly, not as the investigation.

What if the evidence shows the employee really is ill?

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

Should the employee be suspended during the investigation?

Take employment law advice on your own facts. As a general rule, though, the great advantage of a covert investigation is that nothing changes until the evidence is in your hands. Suspending first announces the suspicion, invites the behaviour to pause, and starts procedural clocks running before you know what you are dealing with.

Get the facts before you act. Describe the situation in a free, confidential first conversation. We will give you an honest view on whether surveillance is justified and, if it is, a fixed quote in writing: send a confidential enquiry.