To put it simply constructive dismissal is where an employee is in effectively forced to quit by the employer as a result of the employer attempting to unilaterally alter the terms of the employment contract. A significant reduction in pay or hours, a change of duties, or a loss of job title and status are all potential triggers for a constructive dismissal.
The primary argument typically advanced by lawyers opposed to allowing paralegals to accept legal aid certificates is that it is preferable in all cases to have a lawyer, as they have a great deal more education and training. By this logic, since doctors have more education than nurses surely they should perform all routine medical tests. The obvious objection one would raise to this argument in a medical context is the same one I advance here: it is a waste of resources to exclusively use the most skilled (and consequently expensive) individuals on simple matters.