Calderbank/without prejudice letters cannot be shown or referred to in court but are there exceptions? If such a letter includes a statement of fact, ie an admission of liability previously denied can this be produced in evidence.
Basically (and somewhat in simplicity as there are written rules) purported "Calderbank" and "Without Prejudice" letters can be concealed from the court only if they relate solely to a settlement.
If the letter refers to any other matter at all it becomes "open" and can be shown to the court.