I think some elements i.e. the lack of support and clear/vision/strategy due to three changes in line manager who all had different views, this has been agreed to some degree (one of my previous line managers raised the same issue) and left to pursue a different role. hindsight being a wonderful thing if I had never changed roles I would still be working happily for this employer and would never consider leaving.
not sure if any elements of constructive dismissal as it was myself who raised the issue, could have kept quiet but it was becoming obvious I was not happy (other colleagues mentioned) and was affecting performance and demeanour, I am also conscious this would affect my 15 direct reports which would be unfair.
Many thanks for your patience. I would not say that there appear to be serious enough reasons to treat this as constructive dismissal and whilst there is nothing stopping you from going down that route and trying your lick, it would be rather risky. So try to avoid having to do this, unless you really believe that the relationship has completely broken down and you have no other option but to resign.
Considering you do not wish to take up a lesser role the way forward would appear to be a mutually agreed exit. Now the issue there is that whilst you can go in with a proposed settlement figure and negotiate around it, no one can force the employer to accept it and in the end you will simply have to agree on soothing which you are both happy to accept. So it is not so much a matter of what would be considered fair in the circumstances, but whether the employer can be persuaded to accept it.
I would say as a minimum you should look at something that you would get had you been made redundant by the employer. So that would include your contractual notice period, which must be at least 12 weeks and a redundancy payment, which would either be the statutory minimum (https://www.gov.uk/calculate-your-redundancy-pay) or an enhanced payment better than that but only if your contract allows for it.
In addition, you could try and negotiate an additional discretionary payment on top of that and that is where the negotiations with the employer would come in. Without direct blaming, in order to remain diplomatic, you should point out the issues that have le to this to make it clear that what has happened is making your position difficult and try to find a way forward with this. You can also use the internal grievance procedure if you want an open and formal procedure to look into what has happened and if there is any blame or anything that can be done to resolve it.
The duty of care would not be linked to your length of service and record, there is a general duty of care but that would extend regardless of the above factors. The issue is still going to be covered by the implied duty of trust and confidence which I mentioned in my earlier answer and you have to identify to what extent the blame can be apportioned on the employer and whether it was something within their control or not. Whilst they should try and find you a suitable role, they may only do that if one is actually available, rather than go out of their way to create one to accommodate you.
Hope this clarifies?