In McKinney v London Borough of Newham the EAT looked at when the three-month time limit starts to run where an individual is alleging he has suffered a detriment for whistleblowing.
Croner have produced a useful case summary....they helpfully conclude with:
'The decision clarifies that time begins to run in detriment for whistleblowing cases in the same way as detriment in discrimination cases. This means it is more difficult for whistleblowers to bring their claims in time when they are not aware of the date of any detrimental decision or failure to act. However, it is also likely, in most circumstances, that a tribunal will find it was not reasonably practicable to do so and will extend the time limit.'