If there are limits to what we can do, that shouldn’t mean we lose the job. To comply with the Equality Act, the law brought in to prevent discrimination, the employer should check whether there are “reasonable adjustments” they can make so that we can do the work
For example, for people who cannot stand for long hours, it might be a reasonable adjustment in a shop to put a chair behind the counter. For something to be a reasonable adjustment, it must definitely help us to do the job and the employer must be able to afford to do it.
This means that what is reasonable will depend on the employer. If a small business has an office on the 4th floor of a shared building, it wouldn’t be reasonable to expect them to put a lift in for a wheelchair user, but it might be reasonable for a small business with steps up to their door to get a ramp.