Where an employer is guilty of a fundamental breach of contract e.g. by bullying an employee or unilaterally changing terms and conditions of employment, the employee is entitled to resign and claim constructive dismissal.
Once a fundamental breach has occurred, there is nothing that the employer can do to cure the breach i.e. it doesn't matter how often or sincerely the employer apologises for their behaviour, it does not prevent the employee claiming constructive dismissal.
A possible escape route for employers has however been provided by the EAT in the recent case of Assamoi v Spirit Pub Company. In this case, there had been long standing issues between the Claimant and his line manager. Events escalated to the point where the employee raised a grievance following what he considered were spurious and malicious disciplinary proceedings instigated by the line manager. The grievance was heard promptly by a more senior manager who upheld the grievance and offered the employee a move to another pub if he wished. The employee, unhappy that the line manager had not been forced to apologise, resigned his employment and claimed constructive dismissal based on the line manager's bullying behaviour.
The behaviour of the line manager, in instigating unjustified disciplinary proceedings, certainly had the potential to be a breach of the implied term of mutual trust and confidence. However, by acting promptly and addressing the grievance effectively, the EAT found that the employer had prevented the complaint escalating to the stage where the bad behaviour of the manager would have justified the employee resigning and claiming constructive dismissal.
While, the above case, does not change the general principle that it is too late to rectify a fundamental breach after the fact, it is a useful illustration of the fact that prompt and effective actions by an employer to address an employee's complaints may well prevent the complaint escalating to a stage where it would justify an employee resigning and claiming constructive dismissal. That after all is the purpose of a grievance process!