Imagine a scenario where pay rises are traditionally given out once a year, and apply from the 1st of that month. Pay day is toward the end of the month but the pay given will include the raise dated from the 1st. Letters confirming the pay rise are supposed to be given out near the start of the month, but in reality, it is more like a few days before payday due to company bureaucracy and under-resourcing.
If somebody gave their notice on the 10th of that month but before receiving the letter, should they still receive the pay rise they had been going to get?
Assume the company policy (not widely known or published - the employee could have no way of knowing it) is that pay rises can be taken away at "any stage in the process" if an employee gives notice. The contract also states that pay reviews are at the company's discretion but no mention of anything else relevant.
It goes without saying that the employee would probably not query the decision, had notice been given before the first of the month in which the pay rise applied from.