1. where a written contract clearly defines an employee's contractual duties he ought normally to be entitled to proceed on the basis that he is not obliged to undertake different duties. Employers cannot resort to an implied term in order to be able to impose what is a unilateral permanent variation of the terms of the contract.
   
2. it is likely to be legitimate to find an implied obligation to undertake a duty which is outside of the express terms of the contract where the circumstances are exceptional, where the requirement to work the duty in question is plainly justified, where the work is suitable and the employee suffers no detriment in terms of contractual benefits or status and where the change in duties is temporary.

editor's note:
The Court of Appeal later dismissed Mrs Luke's appeal against the judgment noted above and came to the same conclusion as the EAT but on different, and simpler, grounds. Mummery LJ held that as their employee, Mrs Luke was obliged to comply with the Council's reasonable requirements - which included their requirement that she accept the Report. Therefore this was a simple case of "no work, no pay", and since Mrs Luke was not performing her duties the Council was under no obligation to pay her (see Luke v Stoke-On-Trent City Council, [2007] EWCA Civ 761 Court of Appeal on 24th July 2007, reported at [2007] ICR 1678 and at [2007] IRLR 777).

For relevant general notes see Implied terms in employment contracts/duties of employee and/or Changes to terms of employment .