Constructive dismissal is a form of unfair dismissal because of an act or omission on the part of the employer that has destroyed the mutual obligation of trust and confidence that underpins the employment relationship. For example you employed an individual 6 months ago to work 5 nights a week; you need to change the working pattern and give the employee 24 hours notice that they will be required to work 5 days rather than 5 nights a week. That is a unilateral variation of contract (ie it has not been agreed with the employee), it is a breach of contract on the part of the employer (because they have changed the working time), and the change is significant and could have a major impact on the individual. The employee could just accept the change but if they cannot accept it because of their own personal circumstances and the employer is not prepared to discuss the change, the employee may feel that their employer has left them with no option but to resign.