A constructive dismissal is where an employee resigns because of some very serious action or failure to act by the employer which causes the employee to reasonably believe that continuation of employment is impossible.
A very serious negative change to your contract that is imposed unilaterally (i.e. without your agreement) by your employer, or a refusal by your employer to improve intolerable working conditions, could be justifiable grounds for resignation triggering a potential claim for constructive dismissal. Every case depends on its own unique facts, so everybody’s situation is different.
Resigning and claiming constructive dismissal is a very high-risk strategy, so unless your conditions have become intolerable, you should explore other ways of resolving the situation first. In any event, you should always take careful advice before deciding to walk out of your job.
Very few tribunal claims succeed and, even if you win, unfair dismissal compensation awards are nowhere near as high as many people think. The median award for unfair dismissal in 2017-18 was just £8,015.