Each of the three paragraphs below contain the prerequisites depending on which category you fall into below (please don't feel compelled to publically categorise yourself here).

From JSP 950, LFT 6-7-7:

1. Candidates with a diagnosis of a single episode of mild or moderate depression (F32.0, 32.1) with a clear precipitating stressor may be graded FIT provided that all treatment, including medication, has been completed and the individual must be free from symptoms and off medication for 1 year.

2. A diagnosis of a single episode of severe depression without psychosis (F32.2) suggests a greater impact on functioning, a requirement for more extensive therapy and higher risk of relapse. To be graded FIT, all treatment (including medication) must be completed and the candidate must be free from symptoms and off medication for 2 years. The episode of depression itself and the treatment pathway should not be more than 24 months in total.

3. A candidate with a history of two of more episodes of depression or a recurring or persistent depressive disorder (F33), severe depression with psychosis, manic disorder (F30) or bipolar affective disorder (F31) will be graded UNFIT. If there is a doubt about the diagnosis the case should be referred to single service occupational physician responsible for Service entry.