What is Legitimate Expectation?

Legal Definition
The doctrine of legitimate expectation was first developed in English law as a ground of judicial review in administrative law to protect a procedural or substantive interest when a public authority rescinds from a representation made to a person. It is based on the principles of natural justice and fairness, and seeks to prevent authorities from abusing power.

The courts of the United Kingdom have recognized both procedural and substantive legitimate expectations. A procedural legitimate expectation rests on the presumption that a public authority will follow a certain procedure in advance of a decision being taken, while a substantive legitimate expectation arises where an authority makes a lawful representation that an individual will receive or continue to receive some kind of substantive benefit. In determining a claim for an alleged breach of a legitimate expectation, a court will deliberate over three key considerations: (1) whether a legitimate expectation has arisen; (2) whether it would be unlawful for the authority to frustrate such an expectation; and (3) if it is found that the authority has done so, what remedies are available to the aggrieved person.

Procedural legitimate expectations have been recognized in a number of common law jurisdictions. In contrast, notwithstanding their acceptance and protection in the UK, substantive legitimate expectations have not been universally recognized. For instance, they have been given effect in Singapore but not in Australia.
-- Wikipedia