The Equality Act 2010* defines a disability as “a physical or mental impairment [which] has a substantial and long-term adverse effect on… ability to carry out normal day-to-day activities.”
That’s it. No set list of conditions that do or don’t count, no strict criteria – it’s basically for each person to consider for themselves.
This enables people to ask for adjustments based on their individual needs, without putting value judgements on what are often very broad diagnostic labels. For example, autistic people are protected against discrimination on the grounds of disability even though many autistic people don’t consider themselves to be disabled. Calling autism a disability is politically controversial**, to the point that if there had been a defined list of disabilities, it could well have been left out to avoid stirring up the arguments – blocking the right to reasonable adjustments for autistic people who may need them in systems designed for neurotypical people. And those autistic people who don’t think “disabled” applies to them aren’t forced to identify as such either!
We also don’t know very much about the exact scientific processes behind autism – but that’s okay, because we still recognise that there’s this group of people who experience a certain set of differences and might need certain types of support as a result. The law is less interested in the details of your condition, and more interested in your additional level of need in an ableist and inaccessible world.
This approach also allows for people with lesser-known conditions or even brand new conditions (such as, for the sake of argument, a new virus which unexpectedly sweeps the world and leaves some people with long-term symptoms) without putting every single diagnosis through a legal process. There are thousands of possible health conditions, and as our understanding improves, diagnostic labels are created and changed on a regular basis. Making legal bodies assess every single condition individually is just unrealistic – and if it were required, entire groups of disabled people would inevitably be left out.
This framing matters, because getting it wrong puts people off even asking for help. I’ve lost count of the number of times I’ve had to reassure autistic friends that yes, they can ask for adjustments at work or in services – because they aren’t sure if they “count” as disabled, they’ve seen debates about whether autism is a disability and weren’t sure if the powers that be had decided yet, or because of the false belief that there’s some official list of disabilities (or disabled people) and if you don’t know about it you must not be disabled enough. (Seriously, so many forms ask if you’re “registered disabled” which in the UK is literally not a thing!) We often think of disability as defined in a rigid, exclusionary way – which conveniently limits the number of people who get the support they need – but the reality is much more open than that.
*This Act applies in England, Scotland and Wales. Northern Ireland instead uses the Disability Discrimination Act 1995, but the definition quoted is exactly the same.
**For what it’s worth, I do consider autism as a disability – I don’t think that’s the same as saying autism is a bad thing, because disability isn’t (always) a bad thing. But some people who follow the same reasoning come to a different conclusion for perfectly understandable reasons, and I don’t think it’s especially relevant to the main argument, so I’m not rehashing it here!