You cannot treat someone less favourably because they have a Protected Characteristic. This is against the law. The Equality Act 2010 states people should be treated equally and fairly. Protected Characteristics are race, age, being pregnant, religion, sex, sexual ordination, gender reassignment (someone changing their gender), marriage or disability.
To treat people differently is to discriminate, meaning you put them at a disadvantage and in an unfair situation. This can be Direct Discrimination, such as saying you will not hire someone because they have a certain condition/disability in the case of Direct Disability Discrimination.
It can also be Indirect, where you put someone at a disadvantage, for example, because you do not make Reasonable Adjustments to stop any disadvantage/difficulty. If, for example, you ask people to do a test but fail to accommodate adjustments, like, if someone is Dyslexic and needs extra time, or the use of a computer or a reader. This would be an example of Disability Indirect Discrimination and is not allowed. Employers must accommodate 'Reasonable Adjustments'. If you have aspects of the job that are difficult for you, they must explore adjustments/modification/altered duties to support your strengths and lessen your difficulties.
Harassment is making the working environment difficult, highlighting aspects of disability and making the person feel inferior (not as good as everyone else).
Discrimination can sadly occur in all aspects of life, including in the workplace but people are becoming more understanding and the Equality Act (2010) is there to stop this unfair treatment, meaning, generally, people are treated well and people can access 'Reasonable Adjustments', such as to make small changes to remove potential barriers due to disability and enable the person to show their abilities. After all, this benefits everyone, as the individual is doing their best work and can show their strengths easier.
Disability Discrimination. https://www.scope.org.uk/advice-and-support/disability-discrimination
Check out this Government clip about disability discrimination.
Fixers explores people's misconceptions, stigma and discrimination that needs to change.