OK I know it shouldn't be so, but consider what claiming constructive dismissal will do for your career future. Yes I know that the company who you are leaving can't overtly give that information in a reference but references can be "read between the lines" and however undeserved, if there is a hint that you might be "trouble" then future employers may want to steer well clear and, lets be honest, the employment market at the moment is giving them plenty of choice.
Unpalateable and un PC advice I know but its something to consider.....