A damp course is designed to provide your ground level walls with the protection they need to provent ground water accessing your home. With out a functioning damp course, your walls will not stop water from accessing the walls at ground level.
This will result in damp walls and damp timbers in your home and causing long term damage. A simple but affective solution would be to remove the affected plastered interior and inject the damp walls with a damp course, providing your home with a much needed damp course.
