A disability is a physical or mental impairment with a substantial, long-term (12 months or more) adverse effect on everyday activities. Autism and ADHD usually qualify, but each is judged on its effects, not the label.
The four-part test
Section 6 of the Equality Act 2010 sets one definition, and a person meets it only if all four parts are present:
- An impairment that is physical or mental. There is no fixed list of conditions.
- A substantial adverse effect, which the Act treats as more than minor or trivial.
- A long-term effect, meaning one that has lasted, or is likely to last, at least 12 months or the rest of the person's life. An effect that is likely to recur still counts.
- An effect on normal day-to-day activities such as reading, concentrating, remembering, travelling, or interacting with people.
Some conditions count automatically. Cancer, HIV infection and multiple sclerosis are a disability from the point of diagnosis, with no need to show any effect on day-to-day activities, and a certified sight impairment is treated the same way (Schedule 1). A progressive condition is covered once it produces an adverse effect that is likely to become substantial, rather than waiting until it already has.
Why a diagnosis does not settle it
The test is functional. It asks how the impairment actually affects someone, not which diagnosis sits on the letter. That cuts both ways for you as an employer. An employee can be disabled under the Act without a formal diagnosis, and a diagnosed employee is not automatically disabled if the substantial, long-term effect on day-to-day activities is not made out.
One rule catches people out: the effect is judged without the help of medication, treatment or coping strategies. So if someone manages their ADHD well on medication, you weigh the effect as it would be if the medication were removed, not the managed version you see at work. This is why Acas says that being neurodivergent will often amount to a disability while still being assessed case by case.
What this means for your duties
Where the test is met, disability is a protected characteristic, and you owe a duty to make reasonable adjustments (section 20). You must also not treat someone unfavourably because of something arising from their disability, known as discrimination arising from disability (section 15). The practical risk is gatekeeping: refusing to act until you are certain the legal label is met. A tribunal decides the label after the event; by then the missed-adjustment claim has already landed.
The safer position is to respond to the difficulties an employee describes and to the adjustment they ask for, rather than treating the legal status as a hurdle they must clear first. If you genuinely need to test the status (for example in a capability or absence process), ask for an occupational health view of the functional effects, not just a copy of the diagnosis.
Where the law comes from
Related
This page is general information, not clinical or legal advice.