These are on the University of Essex's website regarding the no-detriment policy.
Safety Net 3
More Flexibility in the Management of Marks and How they Contribute to the Module Outcome
Where you have already met the learning outcomes for a module based on assessment you have already passed, the Alternative Assessment can only improve your module aggregate.
Where you have not yet completed or passed enough assessment to meet the learning outcomes for a module, you will need to complete the upcoming assessments to be able to pass this module. Safety Net 4 means that all students’ performance in the module will be reviewed.
Safety Net 4
Monitoring Module Cohorts Against Previous Three Years
We will be actively comparing module marks this year with the previous three years to ensure that the marks are in line with previous achievement.
The Board of Examiners will look at the performance of students on your module as a whole. If your module cohort performs more poorly than we would expect based on the last three years of students taking that module, we will consider the marks to ensure that you are not disadvantaged.
So I'd guess permitting you did well in years 1&2, you should be considered for a review of your grades, and in turn get a better overall grade for the year no matter if your dissertation only gets a pass.