A waiver of remuneration happens when a director or an employee gives up their right to salary or other cash remuneration and gets nothing in return. Where the employee gets a non-cash benefit in return, this is called a salary sacrifice.
The treatment of a waiver of remuneration, when a director / employee gets nothing in return, is different to the scenario when this is treated as a salary sacrifice.
The effect of a waiver for Income Tax purposes depends on its timing.
The view taken by HMRC is supported by case law decisions, including the cases of Parker v Chapman (13TC677) and Reade v Brearley (17TC687) quoted in the Employment Income Manual.