In order for there to be a substantive or procedural legitimate expectation based on a practice, what is required is that there must be a practice which is impliedly tantamount to a practice.
As with a promise, that practice must give rise to a representation which is clear, unambiguous and devoid of any relevant qualification. Although an express promise is not required, to found a legitimate expectation, there must be a consistent practice which is sufficient to generate an implied representation to the same effect. So stated in R (Heathrow Hub Ltd) v SoS for Transport (2020) EWCA Civ 213 at paragraphs 69 and 75.