I guess you are using the Grievance Procedure? (if you aren't the process should be formalised, and in writing, plus keep your own notes of the meetings).
A Grievance Procedure should have a final appeal at the end of it, and the process document should detail the timescale by which the company will deal with these matters.
So much for the prelims. The answer to the Constrictive Dismissal question is no-one can know for sure, because we don't have all the facts and just your side of the story (which does sound very reasoned). Based on what I know, I would think you might have a reasonable case, but (as I think you know) it is a high-risk strategy because you have to resign and claim constructive dismissal in the letter of resignation.
If you are going to do that anyway, then you have nothing (more) to lose, and potentially a lot to gain.
I suspect that the real decison-makers in the higher echelons of the organisations do not yet realise the importance of this reversal of their decision to you (moving house, another business commitment etc). That is why you should try to use the Appeal procedure to get past the 'yes' men and to the decision-makers.