Yes, unless it was issued in bad faith or was manifestly inappropriate, says the Court of Appeal in Davies v Sandwell. Otherwise, past warnings should not be reconsidered.
This must be right. It has always generally been the case that Employment Tribunals have been very reluctant to reconsider or look behind a previous written warning when considering the fairness of an employers later dismissal particularly if the employee never appealed it at the time.
At least it is now possible to ask a Tribunal to reconsider the fairness of a previous written warning in particular circumstances. This will be of particlar signifcance to employees who have been dismissed whilst on a Final Written Warning that itself was issued in dubious circumstances.