it is an enormous grey area
Hardly...it is point of employment law and as such is defined in very great detail.
Whether a legal eagle could make such a case stick would depend on three things...
- Whether there is a viable case.
- Whether your legal eagle knows his/her stuff.
- How deep your pockets are (somebodies gotta pay and you ain't getting legal aid for this)
According to the last briefing from a law firm I saw (about two years ago) bringing constructive dismissal cases in the UK has become more difficult in recent years.
Anything is worth a try though..if you have the money (and motivation).