For a successful constructive dismissal claim the resignation must be because of the breach and should occur very quickly after the breach or after the final incident. If left too long, the court or tribunal will find that the employee has waived the right to claim constructive dismissal.
The most common problems in showing constructive dismissal is proving that the term breached is sufficiently serious and that the employee had acted quickly enough after the incident complained of. It is often an uphill battle to prove constructive dismissal and, even if it is proven, there is still a need to show the dismissal is unfair, which makes it a two hurdle race.
If you think you may have issues which could give rise to constructive dismissal then it is imperative to get fast and practical legal advice.